Electrodeposition of Pt-Ru nanoparticles on fibrous carbon substrates in the presence of nonionic surfactant: Application for methanol oxidation

Liquid crystalline and micellar aqueous solutions of the nonionic surfactant Triton X-100 were used to direct the electrodeposition of Pt-Ru nanoparticles onto graphite felts, which were investigated as novel anodes for the direct methanol fuel cell. The effects of surfactant concentration, current density and deposition time in the preparation of these three-dimensional electrodes were studied in a factorial experiment and the electrodes were characterized by SEM and ICP-AES. Cyclic voltammetry, chronoamperometry and chronopotentiometry were carried out to assess the activity of the catalyzed felts for methanol oxidation. The presence of Triton X-100 (40-60 wt.%) coupled with an acidic plating solution were essential for the efficient co-electrodeposition of Ru in the presence of Pt to yield approximately a 1:1 Pt:Ru atomic ratio in the deposit. The highest mass specific activity, 24 A g⁻¹ at 298 K (determined by chronoamperometry after 180 s at 0 V versus Hg/Hg₂SO₄, K₂SO_4std), was obtained for the Pt-Ru electrodeposited in the presence of 40 wt.% Triton X-100 at 60 A m⁻², 298 K for 90 min. Surfactant mediated electrodeposition is a promising method for meso-scale (ca. 10-60 nm diameter) catalyst particle preparation on three-dimensional electrodes.     

Study on the electrochemical behaviour of the anticancer herbal drug emodin

The electrochemical behaviour of the anticancer herbal drug emodin was investigated by cyclic voltammetry (CV) at glassy carbon electrode. In 0.05 M NH₃-NH₄Cl (50% ethanol, pH 7.2) buffer solution, a pair of quasi-reversible redox peaks at potentials of Ep1 = −0.688 V and Ep2 = −0.628 V and one irreversible anodic peak, which was a typical anodic peak of emodin, at Ep3 = −0.235 V appeared at a scan rate of 100 mV/s. The irreversible anodic peak currents are linearly related to the emodin concentrations in a range from 8.9 × 10⁻⁸ M to 7.8 × 10⁻⁶ M with a pre-concentration time of 80 s under −0.620 V. Using the established method without pretreatment and pre-separation, emodin in herbal drug was determined with satisfactory results. Moreover, the electrode process dynamics parameters were also investigated by electrochemical techniques.     

Thermolysis of the polyyne C8H2 in hexane and methanol: Experimental and theoretical study

The mean lifetimes of polyyne C₈H₂ in hexane were determined at 50, 60, 80, and 100 °C and in methanol at 60 °C. The reactions are second order at all temperatures: ln k₂ = 20.5 ± 1.5-10303 ± 520T⁻¹ and the corresponding activation energy is 85.7 ± 6.3 kJ mol⁻¹ (7164 cm⁻¹). Extrapolation suggests that solutions at 1 mM concentration are significantly unstable at room temperature. Quantum chemical calculations show that polyynes C_mH₂ + C_nH₂ (m + n = 16) could be products, but these were not detected. Alternatively, C₁₆H₂ isomers could form. IR spectra of the solid residues from hexane and methanol solutions were obtained.     

The fluorescence resonance energy transfer between dye compounds in micellar media

The fluorescence resonance energy transfer from fluorescein to merocyanine 540 in aqueous sodium dodecyl sulfate, cetyltrimethylammonium bromide and Triton X-100 micellar solutions as well as deionized water was investigated at room temperature using steady-state and time-resolved fluorescence spectroscopy techniques. Fluorescence resonance energy transfer rate constants (k_T), obtained using both Stern–Volmer and Förster theories, were in good agreement. Moreover, energy transfer efficiency values of 0.14, 0.38, 0.77 and 0.85 for deionized water, sodium dodecyl sulfate, TX-100 and cetyltrimethylammonium bromide micellar solution were obtained at the highest acceptor concentration at which fluorescence resonance energy transfer was achieved. The data obtained from steady-state absorption, fluorescence spectral studies and time-resolved lifetime measurements indicated that the fluorescence resonance energy transfer from fluorescein to merocyanine 540 occurred most effectively in aqueous cetyltrimethylammonium bromide micellar solutions.     

Surface characterization by X-ray photoelectron spectroscopy and cyclic voltammetry of products formed during the potentiostatic reduction of chalcopyrite

Surface characterization of the transient products that precede chalcocite formation during chalcopyrite reduction was carried out. The experimental strategy employed in the present work consisted of the application of different potential pulses (fixed energetic conditions) on the surface of chalcopyrite electrodes in 1.7 M H₂SO₄. The chemical products formed at different potential pulses were characterized by cyclic voltammetry (CV) and XPS. Each electrogenerated species presented a specific voltammetric behavior and an XPS spectrum, in which the values of principal photoelectronic peak bond energies for Cu 2p_3/2, Fe 2p_3/2 and S 2p_3/2 and the atomic concentrations were considered. Several potential intervals could be identified: in 0.115 ≥ E_cat ≥ −0.085 V vs. SHE, an intermediate copper sulfide is formed whose composition is between those of chalcopyrite and bornite, such as talnakhite. The reduction of this product occurs slowly, giving bornite at potentials less than −0.085 V. In the applied potential region −0.085 ≥ E_cat > −0.185 V, the bornite gradually decomposes causing the incomplete conversion to chalcocite. In the potential interval −0.185 > E_cat ≥ −0.285 V, energetic conditions are large enough to allow the immediate decomposition of bornite, forming chalcocite in a more quantitative manner.     

Electrochemical properties of porous bismuth electrodes

The properties of Bi surfaces with different roughnesses were characterized by electron microscopy, cyclic voltammetry, and impedance spectroscopy. Two different strategies were used for preparation of porous bismuth layers onto Bi microelectrode surface in aqueous 0.1 M LiClO₄ solution. Firstly, treatment at potential E < −2 V (vs. Ag|AgCl in sat. KCl) has been applied, resulting in bismuth hydride formation and decomposition into Bi nanoparticles which deposit at the electrode surface. Secondly, porous Bi layer was prepared by anodic dissolution (E = 1 V) of bismuth electrode followed by fast electroreduction of formed Bi³⁺ ions at cathodic potentials E = −2 V. The nanostructured porous bismuth electrode, with surface roughness factor up to 220, has negligible frequency dispersion of capacitance and higher hydrogen evolution overvoltage than observed for smooth Bi electrodes.     

Kinetics and mechanism of oxygen reduction at hydrous oxide film-covered platinum electrode in alkaline solution

This study uses rotating ring-disk electrode (RRDE) and linear sweep voltammetry (LSV) to characterize oxygen reduction kinetics in alkaline solution on platinum electrodes with various thickness of hydrous oxide (oxyhydroxy) film. Oxyhydroxy films are created on Pt electrodes by pretreatment in 1.0 mol dm⁻³ KOH at a constant voltage. The pretreatment voltage ranges from −1.2 to 1.0 V and is increased stepwise before each new experimental run to produce seven discreet films. LSV plots show oxyhydroxy film thickness strongly inhibits oxygen reduction and is inversely proportional to RRDE oxygen reduction current I_D for LSV voltages E_D from −0.1 to −0.46 V, but this trend reverses at E_D more negative than −0.46 V so that the worst-performing electrode becomes the best. However, this improvement disappears at around −0.8 V, suggesting this change involves a negatively charged ion, possibly embedded into the metal in the top few atomic layers either interstitially or substitutionally. The 1.0 V-pretreated electrode in the E_D range from −0.46 to −0.9 V of highest oxygen reduction current also exhibits the lowest hydrogen peroxide production, with zero H₂O₂ produced at −0.6 V, indicating the brief presence of the oxyhydroxy film on the Pt surface has strong lingering effects. The post-oxyhydroxy Pt surface is very different than the native Pt for oxygen reduction pathway and efficiency. Reaction order with respect to oxygen is close to 1. The rate constants of the direct O₂ to H₂O electroreduction reaction are increased with decreasing the potential from −0.2 to −0.6 V, but the O₂ to H₂O₂ electroreduction is contrary to this expectation. The rate constants of H₂O₂ decomposition on the oxyhydroxy film-covered Pt electrode are near constant around 1 × 10⁻⁴ cm s⁻¹ at E_D > −0.5 V.     

Rapid formation of high-quality self-assembled monolayers of dodecanethiol on polycrystalline gold under ultrasonic irradiation

Self-assembled monolayers of dodecanethiol (C₁₂SH-SAMs) on polycrystalline gold were prepared under ultrasonic irradiation at 100 W (the actual ultrasonic power intensity is about 0.1 W cm⁻² including the heat loss) for different time and investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). CV experiments show that the differential capacitance C_d values of the C₁₂SH-SAM prepared under ultrasonic irradiation at 100 W (0.1 W cm⁻²) for 15 min are independent of the scan rate, the thickness d value of this monolayer is 17.5 Å, the tilt angle φ value of the molecules in this monolayer from the gold surface normal was calculated to be 30° and the difference value of the current density at −0.2 and 0.5 V (Δi_p) is only 0.69 μA cm⁻². From the EIS experiments, we find that the phase angle value at 1 Hz Φ_1 Hz of the C₁₂SH-SAM prepared under ultrasonic irradiation at 100 W (0.1 W cm⁻²) for 15 min is 89°, the charge transfer resistance R_ct value of this monolayer is 1.40 × 10⁶ Ω cm² and the surface coverage θ value of this monolayer was calculated to be 99.997% from R_ct. These results indicate that the C₁₂SH-SAM of almost defect-free structure and very low ionic permeability can be formed under ultrasonic irradiation at 100 W (0.1 W cm⁻²) in a short time (15 min).     

Effect of 1-pentanol on the styrene emulsion polymerization

The influence of 1-pentanol (C₅OH) on the ST emulsion polymerization mechanisms and kinetics is investigated. The CMC of the ST emulsions first decreases rapidly and then levels off when the C₅OH concentration ([C₅OH]) increases from 0 to 72 mM. The effect of C₅OH increases to a maximum and then decreases when the SDS concentration ([SDS]) increases from 2 to 18 mM. At [SDS]=2 mM, homogeneous nucleation controls the polymerization kinetics regardless of [C₅OH]. At [SDS]=4 mM, the effect of [C₅OH] appears due to the transition from homogeneous nucleation to a mixed mode of particle nucleation (homogeneous nucleation and micellar nucleation) occurs when [C₅OH] increases from 0 to 72 mM. The effect of [C₅OH] is the strongest at [SDS]=6 mM since the particle nucleation mechanisms span homogeneous nucleation (low [C₅OH]), a mixed mode of particle nucleation (homogeneous nucleation and micellar nucleation) (medium [C₅OH]) and micellar nucleation (high [C₅OH]). At [SDS] >6 mM, in which micellar nucleation controls the polymerization kinetics, the effect of [C₅OH] decreases rapidly with increasing [SDS].     

Electropolishing of NiTi shape memory alloys in methanolic H2SO4

The electropolishing of NiTi shape memory alloys was surveyed electrochemically. Anodic polarization of NiTi up to 8 V was performed in various aqueous and methanolic H₂SO₄ solutions. The passivity could be overcome in methanolic solutions with 0.1 mol dm−3≤CH₂SO₄≤7 mol dm−3. The dissolution kinetics was studied in dependence of the polarization potential, the H₂SO₄-concentration, the water concentration and the temperature. For lower concentrations of sulfuric acids (CH₂SO₄≤0.3 mol dm−3) electropolishing conditions were not observed for potentials up to 8 V. The dissolution remained under Ohmic control. In the concentration range from 1 to 7 mol dm⁻³ a potential independent limiting current was registered depending linearly on the logarithm of concentration. The best results were obtained with a 3 mol dm⁻³ methanolic sulfuric acid at 263 K which yielded an electropolishing current of 500 A m⁻² at a potential of 8 V. Surface roughness as well as current efficiency showed an optimum under these conditions.     

Electrochemical behavior of LiCoO2 in a saturated aqueous Li2SO4 solution

The electrochemical behavior of a commercial LiCoO₂ with spherical shape in a saturated Li₂SO₄ aqueous solution was investigated with cyclic voltammetry and electrochemical impedance spectroscopy. Three redox couples at E_SCE = 0.87/0.71, 0.95/0.90 and 1.06/1.01 V corresponding to those found at ELi/Li⁺=4.08/3.83, 4.13/4.03 and 4.21/4.14 V in organic electrolyte solutions were observed. The diffusion coefficient of lithium ions is 1.649 × 10⁻¹⁰ cm² s⁻¹, close to the value in organic electrolyte solutions. The results indicate that the intercalation and deintercalation behavior of lithium ions in the Li₂SO₄ solution is similar to that in the organic electrolyte solutions. However, due to the higher ionic conductivity of the aqueous solution, current response and reversibility of redox behavior in the aqueous solution are better than in the organic electrolyte solutions, suggesting that the aqueous solution is favorable for high rate capability. The charge transfer resistance, the exchange current and the capacitance of the double layer vary with the charge voltage during the deintercalation process. At the peak of the oxidation (0.87 V), the charge transfer resistance is the lowest. These fundamental results provide a good base for exploring new safe power sources for large scale energy storage.     

Direct determination of Cu and Fe in jet fuel by electrothermal atomic absorption spectrometry with injection of sample as detergent emulsions

This paper reports the development of a method for the determination of copper and iron in jet fuels employing the electrothermal atomic absorption spectrometry (ETAAS). In order to allow the direct determination of the analytes, the samples were injected into the graphite furnace as detergent emulsions in order to avoid their volatilization during analysis. The results obtained in this work indicated that a stable emulsion can be formed by mixing 1 mL of a 7% m/v Triton X-100 solution containing 10% v/v HNO₃ with 4 mL of jet fuel. The injection of emulsions provided integrated absorbance signals with suitable sensitivity and precision for 300 min at least. The addition of chemical modifier was not necessary because background values were always very low, allowing the use of pyrolysis temperature around 1000 °C for both analytes. Both Triton X-100 and HNO₃ concentrations in the solution used to form the emulsion had remarkable influence on the sensitivity as well as the heating rate employed in the drying step. Under the best conditions established in the present work, limits of detection of 0.50 and 0.46 μg L⁻¹ were observed for copper when oil-based and aqueous standards were added to the emulsions for calibration, respectively. For iron, the limits of detection were 0.88 and 0.90 μg L⁻¹ for oil-based and aqueous standards, respectively. The method was applied in the determination of Cu and Fe in five samples of jet fuels and a recovery test was performed, producing recovery percentages between 95% and 105%.     

Electroanalytical determination of TBHQ, a synthetic antioxidant, in soybean biodiesel samples

This paper reports an electroanalytical method developed for tert-butylhydroquinone (TBHQ) determination in biodiesel in the presence of surfactant Triton X-100 (T-100). T-100 was shown to improve the electroanalytical signal and its use was decisive for direct analysis of TBHQ in biodiesel, only requiring previous dilution of biodiesel samples in methanol. Several parameters were studied and optimized for the development of this methodology. Under optimal conditions, oxidation peak current was proportional to TBHQ concentration in the range of 1.05-10.10 × 10⁻⁶ mol L⁻¹, with limits of detection and quantification of 3.43 × 10⁻⁸ mol L⁻¹ and 1.14 × 10⁻⁷ mol L⁻¹, respectively, by square wave voltammetry (SWV). The results achieved with the proposed method were satisfactory, relative to those obtained using high-performance liquid chromatography (HPLC).     

Influence of halides on the dissolution and passivation behavior of AZ91D magnesium alloy in aqueous solutions

The electrochemical behavior of AZ91D in various aqueous sodium halide solutions was investigated using open-circuit potential (E_oc), potentiodynamic polarization and ac impedance (EIS) techniques. Generally, the results reveal that during immersion a protective layer of a salt film is formed on the alloy surface whose passivation performance depends on the halide nature, its concentration and temperature. E_oc shifts positively with time until attaining a steady (E_st) value, which becomes less noble with increasing concentration or temperature of the test solution. At any given conditions, self-passivation was found to be favored in the order F⁻ > I⁻ > Br⁻ > Cl⁻. This sequence is consistent with that for surface film resistance (R_T) and its relative thickness (1/C_T). Nevertheless, in F⁻ medium each of the above parameters increases with [F⁻] up to a critical value of 0.3 M then decreases. Increasing concentration above 0.3 M induces large change in the microstructure of the outermost layer of the fluorinated extremely protective film and depassivation behavior predominates. In Br⁻ and I⁻ solutions, as well as the lower Cl⁻ concentrations (≤0.01 M), AZ91D exhibits pseudo-passive state over the polarization range from the corrosion potential (E_corr) to the knee point (E_pt) in the anodic scan, at which passivity breakdown occurs with rapid increase in the anodic current and hydrogen gas reaction. At Cl⁻ concentrations >0.01 M the negative difference effect (NDE) occurs under cathodic polarization where E_pt lies negative to E_corr. Addition of F⁻ to the Cl⁻ solution can induce large changes in the behavior of AZ91D. Equal concentration addition (1:1) produces the highest propensity of the surface to form passivating layer that can afford better protection.     

Characterisation of activated nanoporous carbon for supercapacitor electrode materials

Commercial nanoporous carbon RP-20 was activated with water vapor in the temperature range from 950 °C to 1150 °C. The XRD analysis was carried out on nanoporous carbon powder samples to investigate the structural changes (graphitisation) in modified carbon that occurred at activation temperatures T ? 1150 °C. The first-order Raman spectra showed the absorption peak at 1582 cm⁻¹ and the disorder (D) peak at 1350 cm⁻¹. The low-temperature N₂ adsorption experiments were performed at −196 °C and a specific surface area up to 2240 m²g⁻¹ for carbon activated at T = 1050 °C was measured. The cell capacitance for two electrode activated nanoporous carbon system advanced up to 60 F g⁻¹ giving the specific capacitance ∼240 F g⁻¹ to one electrode nanoporous carbon ∣1.2 M (C₂H₅)₃CH₃NBF₄ + acetonitrile solution interface. A very wide region of ideal polarisability for two electrode system (∼3.2 V) was achieved. The low frequency limiting specific capacitance very weakly increases with the rise of specific area explained by the mass transfer limitations in the nanoporous carbon electrodes. The electrochemical characteristics obtained show that some of these materials under discussion can be used for compilation of high energy density and power density non-aqueous electrolyte supercapacitors with higher power densities than aqueous supercapacitors.     

Potential control characteristics of short-chain thiols of thioctic acid and mercaptohexanol self-assembled on gold

In this article we systematically investigated self-assembly of short-chain thiols of thioctic acid (TA) and mercaptohexanol (MCH) on gold under potential control, E_dc (−0.4, +0.4 and +0.7 V) and compared the results obtained with open circuit potential (E_OCP). Effect of E_dc on thiol self-asembly was inspected based on the changes in electrochemical parameters including interfacial capacitance (C), phase angle (Φ_1Hz), current density difference (Δi), charge transfer resistance (R_ct) through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Experimental results showed that E_dc could not obtain stable short-chain self-assembled monolayers (SAMs) (TA and MCH) in a short time. Both TA and MCH had slow self-assembly dynamics and needed a long time (> 24 h) to achieve adsorption equilibrium. Furthermore, the negative potential E_dc (−0.4 V) did not facilitate the ordering of SAMs. The ordering of TA-SAMs was found to be the best when assembled under E_dc (+0.4 V), whereas that of MCH-SAMs was almost the same when assembled under either E_OCP or E_dc (+0.4, +0.7 V). We considered that permeation of ions and water molecules perhaps dominated the slow self-assembly dynamics of short-chain thiols (TA and MCH) under E_dc and mutual interaction between adjacent chains of thiols played an important role in the ordering of SAMs.     

Evaluation and origins of the difference between double-layer capacitance behaviour at Au-metal and oxidized Au surfaces

In studies of processes at oxidized compared with unoxidized electrode surfaces by transient methods corrections for double-layer charging are usually required and have often been made by extrapolation of double-layer capacitance (C_dl) data for the metallic surface, e.g. at Au or Pt, into the potential region of oxide-film formation. Voltammetry and impedance spectroscopy provide direct information on C_dl values determined at unoxidized, i.e. metallic, Au surfaces compared with those of anodic oxide films generated potentiostatically to various extents that are stable in time, and characterized by reductive linear-sweep voltammetry. C_dl is derived from constant-phase element (CPE) values and the CPE parameter, ?, which is near unity for most conditions. At oxidized Au surfaces C_dl depends on potential for various extents of oxide formation; it increases from 15 (±1) μF cm⁻² at 1.75 V (RHE) to 25 (±1) μF cm⁻² at 1.45 V (RHE) and is independent of added Cl⁻ or Br⁻ for concentrations 0-10⁻³ M of both anions, while, at unoxidized Au electrodes in the absence of halide anions, C_dl has a maximum value of 60 (±2) μF cm⁻² at 0.80 V (RHE) and is now dependent on concentration of added Cl⁻ or Br⁻ ion. These major differences of C_dl for the oxidized and unoxidized Au surfaces indicate that double-layer charging corrections cannot be made simply by extrapolation of C_dl data for unoxidized Au metal surfaces into the potential region for oxide formation.     

Multi-element determinations of N,N-dimethylformamide (DMF) coal slurries using ICP-OES

A slurry nebulisation technique was applied for elemental analysis of bituminous coals SARM 18, SARM 19 and four coals from three different seams in Witbank, South Africa, by inductively coupled plasma optical emission spectroscopy (ICP-OES). Major elements (Al, Ca, Fe, Mg, S, Si and Ti) and trace elements (Ba, Cr, Mn, Ni, Sr, V, Zn and Zr) in coal were determined. Various slurry preparations were evaluated using two dispersants (glycerol and Triton X-100) and by varying the concentration of dispersants, between 0.1% and 1.0% (v/v). The effect of initially solubilising the ground coal in N,N-dimethylformamide (DMF) was investigated by varying the volume of DMF added. The effect of wet grinding with DMF was investigated. Wet grinding with DMF was shown to drastically reduce particle sizes (50.0% < 0.28 μm and 90.0% < 6.17 μm) as compared to dry grinding (50.0% < 5.25 μm and 90.0% < 11.1 μm). The reduced particle sizes and increased transport efficiency of the coal slurries led to improved analytical recoveries of elements in the reference coal, SARM 18. The best analytical recoveries for all elements were achieved using 0.1% Triton X-100 with 10.0% DMF. Results obtained by ICP-OES after wet grinding of the coal with DMF, using 0.1% Triton X-100, also gave excellent recoveries (Al, 100%; Ca, 103%; Cr, 106%; Fe, 102%; Mg, 100%; Mn, 104%; Ni, 109%; Si, 102%; Ti, 95.0%; and V, 108%). The results obtained with 10.0% DMF and 0.1% Triton X-100 were in agreement with certified values for all selected elements according to paired t-test at the 95.0% confidence level. Selected elements (Al, Ca, Fe, Mg, Mn, Si, Ti and V) were also analysed with X-ray fluorescence for comparison with results obtained from ICP-OES. Analysis by ICP-OES of microwave digested coal was also carried out. It is suggested that the DMF slurry technique could be used for routine analysis of bituminous coals.     

Stabilization of aviation gasoline as detergent emulsion for lead determination by electrothermal atomic absorption spectrometry

The present work reports the development of a method for the determination of lead in aviation gasoline samples by electrothermal atomic absorption spectrometry (ETAAS). The samples were emulsified before injecting into the spectrometer in order to avoid the high instability observed in the signals when the samples were injected directly without any treatment. Stable detergent emulsions were obtained by mixing 1 mL of a 7% m/v Triton X-100 solution containing 10% v/v HNO₃ with 4 mL of aviation gasoline. These emulsions generated constant integrated absorbance signals for 5 h at least. Several parameters related to the emulsion formation (Triton X-100 and HNO₃ concentrations) and temperature program (pyrolysis and atomization temperatures and heating rate and the final temperature of the drying step) were evaluated. Both Triton X-100 and HNO₃ concentrations in the solution used to form the emulsion influenced the sensitivity of the lead measurements as well as the heating rate utilized in the drying step. The use of a chemical modifier was necessary, being that the Pd conventional modifier presented better performance than the permanent Ir modifier. The limits of detection and quantification derived for the methodology were 1.2 and 4.0 μg L^− 1. Six samples of aviation gasoline were analyzed and the lead concentrations varied between 11.6 and 64.2 μg L^− 1. A recovery test was performed in order to attest the accuracy of the procedure and recovery percentages between 88 and 112% were observed.     

Effects of octylglucoside and triton X-100 on the kinetics and specificity of carnitine palmitoyltransferase

The effects of octylglucoside on the substrate specificity, kinetics and aggregation state of purified carnitine palmitoyltrasferase (CPT) from beef heart mitochondria were investigated and compared to the effects of Triton X-100. Conditions in which CPT can be assayed in the absence of micelles and albumin, thereby eliminating miceller effects on the kinetic parameters, are described. When octylglucoside is substituted for Triton X-100, the specificity of CPT in the forward direction shifts towards the long-chain acyl-CoAs, and large changes in the kinetic constants are observed. The K_0.5 for L-carnitine varied as much as 50-fold, depending on the acyl-CoA and detergent used. At pH 8.0 and 200 μM palmitoyl-CoA, the K_0.5 for L-carnitine is 4.9 mM in 12 mM octylglucoside and 0.2 mM in 0.1% Triton X-100. Octylglucoside enhances the activity of CPT with long-chain acyl-CoA and lowers the K_0.5 for these substrates. At pH 6.0, the K_0.5 for palmitoyl-CoA is 24.2 μM in 0.1% Triton X-100, in contrast to 3.1 μM in 12 mM octylglucoside. Octylglucoside is a competitive inhibitor of CPT with octanoyl-CoA as substrate with a K_i of 15 mM. Nonlinear kinetics for both acyl-CoAs and L-carnitine are observed when the concentration of octylglucoside is reduced to less than half of its critical micellar concentration (cmc). Gel filtration of CPT in octylglucoside below its cmc gives a single protein peak with a molecular mass of ca. 660,000 daltons. These data indicate that the catalytically active form of purified CPT is an aggregate that has quaternary structure and must have a very flexible catalytic site whose affinity for substrate and catalytic efficiency can be altered greatly by changes in environment and experimental conditions.