Presence Of Dodecyl Sulfate Research Articles

Studying the Effect of Cross-Linking and Sulfonation on the Calcium-Binding Ability of Polystyrene Sulfonate in the Presence of Dodecyl Sulfate

Calcium ions in hard water deteriorate the cleaning performance of detergents by interacting with the anionic surfactants and inducing their precipitation. Polystyrene sulfonate is a common component of cation-exchange resins that adsorb hard ions such as Ca+2 and Mg+2, which adhere to the sulfonate groups. Therefore, understanding the calcium-binding ability of polystyrene sulfonate in the presence of dodecyl sulfate can help in designing novel water-softening agents for applications related to detergency. Studying the association between polystyrene sulfonate and dodecyl sulfate via calcium ion bridges is also important. Since resins contain cross-linked polystyrene sulfonate, degrees of cross-linking and sulfonation are two important parameters. We use molecular dynamics simulations to study the effect of the above parameters on the calcium-binding ability of isotactic polystyrene sulfonate in the presence of dodecyl sulfate. We observe negligible dependence of calcium-ion binding of polystyrene sulfonate on the degrees of cross-linking and sulfonation. The formation of calcium ion bridges between cross-linked polystyrene sulfonate and dodecyl sulfate is strongly affected by the degree of sulfonation. Such bridges are observed more for the intermediate degrees of sulfonation. This is because, at a very low degree of sulfonation, dodecyl sulfate ions align closer to the cross-linking aromatic groups than the sulfonated ones. On the other hand, at high degrees of sulfonation, stronger electrostatic repulsion disfavors the proximity between dodecyl sulfate and polystyrene sulfonate.

Effect of Tacticity and Degree of Sulfonation of Polystyrene Sulfonate on Calcium-Binding Behavior in the Presence of Dodecyl Sulfate

The hardness-causing ions like calcium are detrimental to the performance of anionic surfactants like dodecyl sulfate. Polystyrene sulfonate is an essential component of ion exchange resins that are used to adsorb such ions. Therefore, understanding the binding behavior of calcium ions to polystyrene sulfonate in the presence of dodecyl sulfate is of industrial relevance. Two important structural parameters of polystyrene sulfonate are known to influence its behavior: (i) The arrangement of aromatic groups around the carbon backbone (tacticity) and (ii) the degree of sulfonation. We use molecular dynamics simulations to study the effect of the above two parameters on the calcium-binding to polystyrene sulfonate in the presence of dodecyl sulfate. We observe that the calcium-binding ability and its response to the dodecyl sulfate are highly sensitive to the arrangement of aromatic groups around the backbone. We identify one atactic structure of 100% sulfonated polystyrene sulfonate and another of 20% sulfonated polystyrene sulfonate that shows a significant increase in calcium ion binding upon the addition of dodecyl sulfate ions. The increase in the 100% sulfonated structure is due to the formation of calcium ion bridges between the sulfonate groups located on one side of the backbone. The increase in the 20% sulfonated structure is due to the increase in the sulfonate-Ca-Cl type of ion bridges. We also observe a stronger association between dodecyl sulfate and low sulfonated polystyrene sulfonate because of the hydrophobic interaction between polystyrene sulfonate’s backbone and the hydrocarbon tail of dodecyl sulfate. However, aligning all the aromatic groups on the same side of the backbone (isotactic structure) sharply weakens the association between the two species. Our results can aid in achieving the desired water softening capacity of ion exchange resins in the presence of anionic surfactants via altering the tacticity and degree of sulfonation.

Using Molecular Simulations to Understand the Effect of Dodecyl Sulfate on the Calcium-Binding Ability of Polystyrene Sulfonate

We demonstrate the potential to tune the binding of calcium ions with polystyrene sulfonate (PSS) in the presence of dodecyl sulfate (DS). This can aid the design of surfactant-responsive water-softening agents for applications in detergency. We use molecular dynamics simulations to study the effect of the concentration of DS ions and the degree of sulfonation on the propensity of calcium ions toward PSS. We observe that the presence of DS ions increases the propensity of calcium ions toward 100% sulfonated PSS. The above phenomenon is due to the hydrophobic attraction between PSS and DS at low DS concentrations and the formation of calcium ion bridges between sulfonate and sulfate groups at moderate to high DS concentrations. We also observe the formation of calcium ion bridges between the sulfonate groups at high DS concentrations. The presence of DS ions also increases the propensity of calcium ions toward 20% sulfonated PSS. This is mainly due to the hydrophobic attraction between PSS and DS ions. The calcium ion bridges between sulfonate and sulfate groups are less prevalent than those of 100% sulfonated PSS. We do not observe calcium ion bridges between sulfonate groups of 20% sulfonated PSS. We use the above-mentioned insights to suggest potential strategies for designing an anionic polyelectrolyte having a suitable calcium-binding ability at a given concentration of the anionic surfactant. Finally, strong PSS-DS affinity is detrimental to the activity of surfactants because less surfactant ions are available for detergency. Our results also indicate the possibility of altering the PSS-DS affinity by changing the degree of sulfonation.

Molecular architecture of highly protective coatings of electrodeposited dodecyl sulfate-doped polypyrrole

The chemical structure and molecular arrangement in polypyrrole coatings electrodeposited in the presence of dodecyl sulfate has been studied using XPS, Raman spectroscopy and linear dichroism in the Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. The as-deposited polypyrrole has two-dimensional structure with a high proportion of dodecyl sulfate anions. This structure contains one dodecyl sulfate anion for each nitrogen atom involved in the formation of charge carrier or supposedly protonated. This corresponds to drastic changes in the N K NEXAFS spectra observed as complete disappearance of π*-related resonances. The dodecyl sulfate doped polypyrrole shows linear dichroism of the carbon edge NEXAFS spectra, indicating a predominantly flat laying orientation of the pyrrole rings and up-right orientation of the dodecyl sulfate ion tails relative to the substrate plane. Such molecular architecture of the electrodeposited dodecyl sulfate-doped polypyrrole provides its very high anticorrosive properties. The duration of the protection in the 3.5% NaCl solution was 850 h for dodecyl sulfate-doped polypyrrole coating, which is 17 times longer than for traditional polypyrrole coating doped with oxalate ions.

Silver nanostructures from Ag(CN) 2 − reduction by citrate ions in the presence of dodecyl sulfate and Cu2+ ions. Synthesis and characterization

The synthesis of silver nanoparticles has been investigated using Ag(CN)2− species as precursor, citrate ions as reducing agent, and dodecyl sulfate ions as stabilizer, at pH 11 and 97 °C, in a batch stirred glass reactor. The role of Cu2+ ions in the synthesis was also studied. Bird-of-paradise flower-type nanostructures composed of AgCN nanowires having inside Ag and AgCN nanoparticles were produced in the absence of Cu2+ ions. The nanostructures slowly grew and transformed to AgCN nanowires with embedded Ag and AgCN nanoparticles, having a mean size of 9.7 ± 3.6 nm. The presence of Cu2+ ions in the synthesis significantly enhanced the production of the nanostructures. Nanowires having a thickness of 63 ± 33 nm and length of up to 20 μm were produced. Cu2+ ions also simultaneously lead to the synthesis of ordinary free Ag nanoparticles with a bimodal size distribution (mean sizes of 9.9 ± 3.9 and 65.5 ± 27 nm) and a low experimental formation kinetic rate constant of 1.22 × 10−4 s−1. Feasible mechanisms are presented for the origin of the AgCN nanowires, Ag and AgCN nanoparticles inside the nanowires, and for the free Ag nanoparticles. UV/Vis spectrometry was used to measure the surface plasmon resonance of the nanoparticles and the synthesis kinetic rate constant of the free Ag nanoparticles. ATR–FTIR spectroscopy, EDS–SEM, EDS–TEM, and HRTEM were used to characterize the size, crystal structure, texture, and chemical composition of the synthesis products.

Electrochemical oxidation mechanism of ambroxol and its voltammetric determination in the presence of dodecyl sulfate

The voltammetric behavior of ambroxol (AMB) at carbon paste electrode (CPE) in acidic aqueous solution was studied in this work. The possible oxidation mechanism was suggested that amine group of AMB underwent a two-electron and two-proton oxidation to produce an anilino-radical at the higher potential around 1V (vs. SCE), showing an irreversible oxidation peak. Subsequently, the anilino-radicals dimerized via ‘head-to-tail’ coupling to yield a corresponding 4-amino-diphenylamine derivative in its oxidized form. This generated dimer was reduced and oxidized in the lower potential range of 0.1–0.39V (vs. SCE), showing a pair of quasi-reversible redox peak. With the mechanism, the different scavenging effect of AMB on reactive oxygen species (ROS) was attributed to that different species of AMB take part in the reaction with ROS. In the case of electrochemical oxidation of AMB, anionic surfactant sodium dodecyl sulfate (SDS) was found to play a dual function in eliminating the electrostatic repulsion between the protonated AMB and the CPE with high positive potential and prolonging the lifetime of the anilino-radical of AMB oxidation. In 0.1M HAc-NaAc buffer (pH 5.0) solution containing 3.0×10−4M SDS, the oxidation peak of amine group of AMB appeared at 0.93V (vs. SCE) and the peak current enhanced by 4.5 times in comparison to that in the absence of SDS. Based on this, a single-sweep voltammetric method was proposed for the determination of AMB. The second-order derivative peak current of AMB was rectilinear with its concentration in the range of 3.0×10−8–4.0×10−7M. The limit of detection was 5.4×10−9M. The sensitivity of the determination of AMB was improved, the oxidation potential of AMB was reduced and the experimental condition was moderated.

Electrochemical polymerization of 3,4-ethylenedioxythiophene in the presence of dodecylsulfate and polysulfonic anions—An acoustic impedance study

PEDOT layers are synthesized in aqueous solutions in the presence of one of the three different anionic species – polysterenesulfonate (PSS), poly(2-acrylamido-2-methyl-1-propane-sulfonate) (PAMPS) and dodecylsulfate without any addition of further inorganic anions. Simultaneous electrochemical and acoustic admittance measurements are carried out in the course of polymerization. The data from the admittance spectra are used to extract information on the mechanical shear storage and loss moduli of the three types of PEDOT layers. The anionic species are found to affect the polymerization kinetics, the surface morphology and most markedly the viscoelastic properties of the three types of layers. The latter depend primarily on the innate structure arising in the course of polymerization whereas the solution specifics play a secondary role. Dodecylsulfate imparts significant stiffness to the PEDOT layers with high rigidity preserved for relatively large polymerization charges. The G moduli in this case exceed 109dyn/cm2. Both polyanion-doped PEDOT layers are found to be softer but there is nevertheless a clear difference between them with PEDOT/PAMPS having a strong predisposition for swelling.

Characterization and friction performances of Co–Al-layered double-metal hydroxides synthesized in the presence of dodecylsulfate

In this paper, Co–Al-layered double-metal hydroxides (CAD-LDHs) were synthesized by co-precipitation in the presence of dodecylsulfate (DDS) and characterized by XRD, FT-IR, TG–DSC, SEM. In addition, their frictional features were evaluated by four-ball friction tester, gear tester and air compressor. The results showed that synthesized CAD-LDHs have a hexagonal platelet morphology. Most crystallites have a disk diameter of around 150–250nm and a thickness of about 20nm, with a0=b0=0.31nm, c0=8.33nm, d-spacing=2.78nm and gallery height=2.30nm. The specific surface area is 78m2/g. DDS anions entered the interlayer of LDHs and were perpendicular to the LDH layer in a monolayer array. As a lubricant, CAD-LDH powder has excellent dispersability and suspension stability in the lubrication oil, and can significantly reduce friction coefficient (50.7%) and wear of friction pairs (17.9%). At the same time, they can reduce the temperature of lubrication oil (6.1%) and power consumption of driving motor (2.6–6.8%). Accordingly, CAD-LDHs may broadly be used as lubrication and anti-frictional materials.

Nanoporous Conducting Polypyrrole Gas Sensor Coupled to a Gas Chromatograph for Determination of Aromatic Hydrocarbons Using Dispersive Liquid–Liquid Microextraction Method

In this work, a dodecylsulfate-doped nano porous polypyrrole gas sensor (PPy-DS) has been prepared by vapor deposition polymerization of pyrrole on surfaces of commercial polymer fiber in the presence of dodecyl sulfate (DS) as an anion dopant. The sensing behavior of PPy-DS in the presence of several aromatic hydrocarbons: benzene (B), ethyl benzene (E), toluene (T), 1,3,5-trimethylbenzene (TMB), and some other volatile organic compounds were studied experimentally. The PPy-DS had demonstrated fast response time ( <; s), sensitive for BTE and TMB with good reproducibility when reused. The sensitivity of the PPy-DS for various organic hydrocarbons was in the following order: BTE, TMB ≫ alcohol, acetone, acetonitrile, chloroform, and carbon disulfide. The PPy-DS coupled to a gas chromatograph and used for speciation determination of BTE and TMB in water samples by using a dispersive liquid-liquid microextraction (DLLME) method.

Polyacetylene nanoparticles-based preparation of polyaniline nanofibers

A conjugated polymer polyacetylene (PA) nanoparticles-based preparative strategy toward doped polyaniline (PANI) nanofibers has been demonstrated for the first time, carried out by chemical oxidative polymerization of aniline under rapid stirring using ammonium persulfate as the oxidant in acidic aqueous media in the presence of dodecylsulfate (SDS)-stabilized PA nanoparticles. It is found that only PANI nanoparticulates are formed when the synthesis is performed in the absence of PA nanoparticles. The optical properties and the electronic conductivity of the resulting doped nanofibers and the corresponding dedoped products were studied and the influence of the amount of PA nanoparticles used on the morphologies of PANI nanostructures was also investigated. A possible mechanism is proposed to explain the formation of the PANI nanofibers.

Structure and catalytic properties of Sn-containing layered double hydroxides synthesized in the presence of dodecylsulfate and dodecylamine

Sn(IV)-containing layered double hydroxide (LDHs) materials were synthesized via a simple co-precipitation method using organic surfactants (sodium dodecylsulfate (SDS) and/or dodecylamine (DDA)) at mild temperatures. All the samples were characterized using X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and thermal analysis (TG-DTA). Their catalytic properties were evaluated using a batch reactor system for the conversion of oleic acid. The experimental results show that the interlayer arrangements of the dodecylsulfate anions were consistent with a vertical bilayer arrangement, and that the nature of the synthesizing organic surfactant used greatly influenced the texture and morphology of synthetic Sn(IV)-containing LDH materials. Moreover, the presence of MgSn(OH) 6 species in the synthesized materials favored the conversion of oleic acid, while the sample synthesized under the presence of the organic surfactant showed an improvement on the selectivity of stearic acid.

Activation and inhibition of phosphorylase kinase by monospecific antibodies against preparatively isolated alpha, beta and gamma subunits.

Homogeneous alpha and beta subunits were isolated for the first time in preparative amounts in the presence of sodium dodecyl sulfate. Analysis by analytical polyacrylamide electrophoresis, sedimentation velocity, and immunoprecipitation with monospecific antibodies indicated homogeneity. The apparent molecular masses of the purified subunits as determined electrophoretically in the presence of dodecyl sulfate are: alpha = 140.2 +/- 2.1 kDa and beta = 123 +/- 1.8 kDa. Amino acid analyses show that per 100 mol amino acid the alpha-subunit has a higher serine content (Ser alpha/Ser beta = 1.32, Ser alpha/Ser gamma = 1.42) and a lower aspartic acid/asparagine (Asx) content (AsX alpha/Asx beta = 0.76, Asx alpha/Asx gamma = 0.90) than the beta and gamma subunits. Monospecific antibodies against the purified alpha, beta and gamma subunits were produced in sheep [J. Immunol. Methods (1984) 70, 193-209] and their action on the catalytic activity of non-activated phosphorylase kinase assayed. It can be shown that certain antibody fractions of anti-alpha, anti-beta and anti-gamma inhibit the Ca2+-dependent and Ca2+-independent activity at pH 6.8 as well as at pH 8.2. Other antibody fractions against the beta and gamma subunits however activate the Ca2+-dependent activity at pH 6.8 threefold to fourfold, although they inhibit the activity at pH 8.2. These antibodies lead to a ca. five fold increase in the pH 6.8/8.2 activity ratio. Activating anti-beta can even overcome the inhibitory action of anti-alpha at pH 6.8. A kinetic analysis shows that inhibition is the result of a mixed type mechanism whereas activation is due to a fivefold to tenfold increase in V for phosphorylase b. The results illustrate the importance of possibly large, concerted conformational changes of phosphorylase kinase. It appears that activation or inhibition can be triggered by the antibody binding to conformational determinants of a single subunit type leading to a structural alteration of the holoenzyme.

Isolation of a Second Rifamycin-Binding from Escherichia coli by Affinity Chromatography

When extracts of Escherichia coli are filtered through a Sepharose column containing covalently bound rifamycin a protein is bound which can be eluted either with a high concentration of urea or more specifically with low concentrations of rifamycins. Its Mr is 18,000 +/- 1,000 in the presence of dodecylsulfate, in its absence 36,000 +/- 3,000. The association constant of the protein for rifampicin is 2.4 +/- 0.5 x 10(-4) M with two binding sites per dimer as determined by equilibrium dialysis. Large amounts of this protein are released from the cells by an osmotic shock.

Activity enhancement of CuZn-impregnated FSM-16 by modification with 1,3-butanediol for steam reforming of methanol1

Sterically hindered phenolic antioxidants (AOs) of the IKhFAN family are characterized as inhibitors of initiated oxidation of methyl oleate in homogeneous chlorobenzene solutions and in aqueous emulsions in the presence of dodecyl sulfate. The IKhFANs inhibit oxidation by scavenging peroxo radicals and by decomposing hydroperoxides to yield molecular products. The effect of an IKhFAN is governed by its chemical structure and by oxidation conditions. The IKhFANs slow down methyl oleate oxidation in lipid solution more effectively than comparable concentrations of α-tocopherol, dibunol, phenosan K, or phenosan ester. The most effective is IKhFAN-10, in which the R3 radical is the shortest (CH3). The inhibiting effect of the AOs weakens markedly with increasing chain length of R3. The specific features of the observed oxidation kinetics are explained by the formation of microheterogeneous systems involving AOs. In these systems, the phenolic OH groups are directed to the micelle center and, as a consequence, can hardly react with RO 2 · radicals. In the IKhFAN group in which R3 ranges from C8H17 to C16H33, the induction period grows in proportion to the number of carbon atoms. In an aqueous emulsion, the overall inhibiting effects of structurally different IKhFANs are similar and weaker than effects in homogeneous solution.

Anaerobic digestion of alcohol sulfate (anionic surfactant) rich wastewater – batch experiments. Part II: influence of the hydrophobic chain length

High-strength wastewater of some industries contains high concentrations of surfactants and readily biodegradable compounds like starch and other carbohydrates. Wastewater of this type is found in the textile wet-processing industry (e.g., cotton desizing). The anaerobic degradation process in such wastewater is inhibited due to the high surfactant content. Alcohol sulfate (AS) of increasing hydrophobic chain length (C 8 to C 18, surfactant) and soluble starch (size) were used as model compounds in a series of batch experiments with high loadings of the biomass (65 g AS/kg cell dry weight; 910 g starch/kg cell dry weight). The strongest inhibition of the hydrolysis, acidogenesis and acetogenesis was found in reactors containing medium chain ASs like dodecyl sulfate. Starch hydrolyzation rates decreased by nearly 90% in the presence of dodecyl sulfate. Decyl sulfate caused the strongest inhibition of the methanogenesis and a decrease of the methane evolution by 75% within 87 days experimental time. It was found that short as well as long chain ASs caused only minor inhibition phenomena. The presented data can be used as a basis for the selection of suitable surfactants that do not (or not seriously) inhibit the anaerobic digestion of industrial effluents.

The simple and rapid spectrophotometric determination of trace chromium(VI) after preconcentration as its colored complex on chitin

Preconcentration method with collection of metal complexes on a chitin has been applied to the spectrophotometric determination of chromium(VI) in water. The chromium(VI) is collected as its 1,5-diphenylcarbazide(DPC) complex on a column of chitin in the presence of dodecyl sulfate as counter-ion. The Cr-DPC complex retained on the chitin is eluted with a methanol-1 M acetic acid mixture (7:3, v/v), and the absorbance of the eluent is measured at 541 nm. Beer’s law is obeyed over the concentration range of 0.05–0.6 μg of chromium(VI) in 1 ml of the eluent. The apparent molar absorptivity is 3.5×10 4 dm 3 mol −1 cm −1. The tolerance limits for Fe(III) is low, i.e. ten times that of chromium(VI), but some metal ions and common inorganic anions do not interfere in concentration range of 100–10 000 times that of chromium(VI). The present method can be applied to the determination of chromium(VI) in natural water samples.

Spectrophotometric determination of cationic surfactants in water samples containing anionic surfactants.

Concerning the spectrophotometric determination of cationic surfactants (CS) with anionic dyes, when a large amount of anionic surfactants (AS) is contained in a water sample, CS can not be determined, because it reacts with AS to form a CS-AS ion associate and doesn't react with anionic dyes. A method is proposed to avoid interference from AS based on the extraction of the CS-AS ion associate formed into an organic solvent from water samples to separate it from any excess of AS and color development by replacing AS in the CS-AS ion associate extracted with anionic dyes. In the presence of dodecylsulfate (LAS) as AS and sodium chloride, CS, such as alkyl trimethyl ammonium salts, tetraalkyl ammonium salts, alkyl dimethyl benzyl ammonium salts and alkyl pyridinium salts, was extracted as the CS-AS ion associate into 1, 2-dichloroethane. When a tetrabromophenolphtalein ethylester dye anion (TBPE) was used at pH8.510 as anoinic dyes, a CS-TBPE ion associate was formed in 1, 2-dichloroethane and was measured spectrophotometrically at 610 nm. The absorbance was propotional to the concentration of CS. Good results were obtained on recovery tests using river and sea water samples containing AS in the range of 0.120.16 mg as LAS/1.

Variability in heat-induced fragmentation of a protein in the presence of dodecyl sulfate: the role of an intramolecular sulfhydryl/disulfide exchange.

alpha-Amylase from Aspergillus oryzae was investigated to better understand how disulfide-bonded proteins behave during denaturation with dodecyl sulfate. It was previously reported that the alpha-amylase, when denatured with dodecyl sulfate, forms two species, D1 and D2. In D1, the disulfide bonds remain intact, while in D2, there is a restricted single sulfhydryl/disulfide (SH/SS) exchange reaction. This phenomenon was re-examined as follows: electrophoretic analysis of fragments created with and without modification of a free SH group or disulfide-reduced SH groups; N-terminal sequence analysis of the fragments; reactivity of a free SH group with Ellman reagent. Data from the former two analyses showed that the variability in the electrophoretic patterns results from cleavage at Asp163-Cys164 or Asp282-Cys283, provided that these Cys residues are reduced. Different reactivities of a SH group in D1 and D2 and the appearance of a polypeptide with a nonnative SS pairing in D2 fragments confirmed that the different electrophoretic patterns result from an intramolecular SH/SS exchange. This rearrangement accounts for the variety of electrophoretic patterns observed with D2 amylase and is a result of the creation of a specific free Cys283. Specifically, the variety appears to be due to the breaking of either Cys150-Cys164 or Cys240-Cys283, which in turn leads to the labilization of Asp163-Cys164 or Asp282-Cys283, respectively.

Modulation of the Behavior of a Protein in Polyacrylamide Gel Electrophoresis in the Presence of Dodecyl Sulfate by Varying the Cations

The denaturation of Aspergillus oryzae α-amylase by dodecyl sulfates can be modulated by the change of cations among sodium, lithium, and several alkanolammonium ions. The denaturation can be detected by polyacrylamide gel electrophoresis in the presence of alkanolammonium dodecyl sulfates, particularly around 0°C where the denaturation reaction can be virtually frozen. The moderate stability of the amylase against denaturation by dodecyl sulfates helped to demonstrate the difference among the cations. We previously reported a significant difference among the dodecyl sulfates in their ability to dissociate chlorophyll-protein assemblies. The present results indicated that there is also a difference in the ability of the dodecyl sulfates to denature the amylase, a monomeric water-soluble protein. Two species, one retaining intact disulfide bonds and the other underwent a single sulfhydryl-disulfide exchange reaction, were generated during amylase denaturation by dodecyl sulfates.

Inhibition of phenol sulfotransferase by pyridoxal phosphate

The biologically abundant cofactor, pyridoxal-5-phosphate (PLP), is a potent inhibitor of bovine phenol (aryl) sulfotransferase (PST). Preincubation of purified enzyme with as little as 1 μM PLP decreased PST activity by 50%. Excess 2-naphthol protected PST from inactivation by PLP, whereas 2-naphthyl sulfate and PAPS were not protective. Although PLP inhibition was apparently competitive with 2-naphthol, a steady-state kinetic K i value could not be measured due to non-linear Lineweaver-Burk plots in the presence of the inhibitor. Kinetic progress curves revealed that this was due to progressive loss of activity during catalysis. The kinetics of inactivation of PST by PLP were pseudofirst-order and exhibited saturation. The derived K I value for the binding of PLP to PST in the initial reversible step was 23 μM, with a maximal rate of inactivation of 0.077 min −1. Absorbance spectra of the PST/PLP complex indicated the formation of a Schiff base conjugate, and this is consistent with decreased electrophoretic mobility of the protein-PLP adduct in the presence of dodecyl sulfate only after reduction with borohydride. These results point to the possible regulation of an important detoxification enzyme by a ubiquitous cofactor.