Studies on the reliability of a novel absorption-lipophilicity approach to interpret the effects of the synthetic surfactants on drug and xenobiotic absorption

Some theoretical principles of the absorption/lipophilicity approach, which attempts to explain the effects of the synthetic surfactants on xenobiotic and drug intestinal absorption, are reviewed and experimentally checked by examining the correlations obtained between "in situ" absorption constants, ka, found in rat colon, and "in vitro" lipophilicity indexes, K', for two compound series (secondary aliphatic amines and phenylalkylamines) in the absence and in the presence of the nonionic surfactant Polysorbate 80, in the intestinal perfusion fluid. Evidence is given for the following actions of the synthetic surfactant: at its critical micelle concentration (CMC), it increases the polarity of the absorbing membrane and, at the same time, it disrupts the aqueous stagnant diffusion layer adjacent to the mucosal barrier. When a supramicellar concentration (SMC) is used, the above actions are almost totally masked by the micellar solubilization of the tested amines, which decreases their absorption constants relative to those found at CMC, as markedly as solute lipophilicity increases. As a consequence of these actions, the correlations between ka and K', which are clearly hyperbolic in free solution, become potential in the presence of the surfactant at its CMC, whereas at SMC a bilinear correlation is obtained. Absorption via lipophilic ionized species seems to take place for both compound series. Mathematical and physicochemical interpretations of this behaviour are outlined, and biopharmaceutical implications of these phenomena are discussed.     

Control of Vaporous Naphthalene by Scrubbing with Surfactants

This study investigates the effects of adding anionic and nonionic surfactants to the scrubbing liquid during the absorption of naphthalene (Nap) using a wet scrubber. Both batch and continuous experiments were performed on a laboratory-scale packed tower scrubber by adding surfactants to the scrubbing liquid. An anionic surfactant sodium dodecyl sulfate (SDS) and two nonionic polyoxyethylene surfactants C10E4 [tetraethylene glycol mono(decyl ether)] and C14E8 [octaethylene glycol mono(tetradecyl ether)] were used. The concentrations of the surfactant solutions all exceeded the critical micelle concentration. The results of continuous experiments indicate that the efficiencies of removal of naphthalene by C10E4 and C14E8 were 75.0 and 71.9%, respectively, at a concentration of 1.0×10?2?M. The removal efficiency of naphthalene by SDS ranged from 6 to 39% at concentrations from 1.0×10?2 to 1.0×10?1?M under continuous scrubbing. In the batch experiments, the batch naphthalene absorption capacities were estimated to be 31.8?μg?Nap/g?C10E4, 12.9?μg?Nap/g?C14E8, and 2.4 μg Nap/g SDS. A comparison was also made among SDS, C10E4, and C14E8 in terms of cost, foaming, impact of wastewater, removal efficiency, and absorption capacity.     

Does routine follow up after head injury help? A randomised controlled trial

Excess surfactant present in emulsions can influence the rates of transport of incorporated drugs by micellar solubilization, alteration of the partitioning process and by drug-surfactant complexation. Cetyltrimethylammonium bromide (CTAB), a cationic surfactant was selected to investigate these phenomena as it forms relatively stable mineral oil-water (O-W) emulsions and has the potential for ionic interaction. Phenylazoaniline, benzocaine, benzoic acid and phenol were chosen as model drugs for this study. The emulsion critical micelle concentration (CMC) for CTAB determined using a combination of a membrane equilibrium technique and surface-tension measurement was 1.0% w/v in 10% v/v% O-W emulsion systems. Ionic interaction between model drugs and surfactants and drug hydrophobicity affected their transport rates in the emulsion systems. The transport rates of the lipophilic drugs (benzocaine and phenylazoaniline) and the ionized hydrophillic drug (benzoic acid, pH 7.0) in the emulsion systems increased with increasing CTAB concentration up to 0.5% w/v micellar concentration and then decreased at higher concentrations. The rate of transport of phenol was not affected by the presence of micellar phase. Ionic interaction between surfactant and model drugs affected transport rates of model drugs in emulsion systems. The micellar phase was considered to affect the overall transport rates of model drugs.     

Enhancing the Biodegradation of Polycyclic Aromatic Hydrocarbons: Effects of Nonionic Surfactant Addition on Biofilm Function and Structure

The application of surfactants for the bioremediation of sites contaminated with polycyclic aromatic hydrocarbons has been widely reported, because they are known to increase PAH solubility and desorption, thereby enhancing their bioavailability to biofilm microorganisms. The effects of a nonionic surfactant on the biodegradation of PAHs in porous media, as well as the fate of the surfactant, were investigated in this study. Column experiments in the presence of the surfactant showed that the degradation of the two-ring PAH alone was not significantly affected, but that there was a small enhancement of three- and four-ring PAH degradation when they were present as sole substrates and when using Triton X-100. This was due to the higher solubility of the PAHs in the presence of the surfactant. Biofilm seemed to respond well to binary mixtures of phenanthrene–naphthalene and pyrene–naphthalene, with removals of 45.5 and 24.1%, respectively, in the presence of the surfactant; however, higher biodegradations were always achieved by having just PAH mixtures without the surfactant, indicating the importance of cometabolic mechanisms over improved solubilization of PAHs. Optical sections taken using a confocal laser scanning microscope allowed observation of a heterogeneous web-like matrix of biofilm, with diverse biological aggregate structures.     

Synthesis and characterization of N-octanoyl-beta-D-glucosylamine, a new surfactant for membrane studies

The new nonionic glycosidic surfactant N-octanoyl-beta-D-glucosylamine (NOGA, molar mass 305.37 g) was synthesized through an easy and efficient two-step procedure. Specifically, beta-D-glucosylamine was obtained by the replacement of the anomeric hydroxyl of D-glucose by an amino group which was then selectively acylated. NOGA was finally purified by silica gel column chromatography and recrystallization. This compound is stable and soluble in water and usual buffers up to 80 mM at 4 degrees C and up to 0.2 M at 37 degrees C. NOGA solutions are also characterized by a low ultraviolet light absorbance above 250 nm (epsilon 280 approximately 1.5 M-1 cm-1). Due to its very high critical micelle concentration (CMC = 80 mM, as determined by spectrofluorimetry), this surfactant may easily be removed from samples by dialysis or, to a lesser extent, by adsorption onto hydrophobic beads. Furthermore, NOGA is colorimetrically titrable by the ninhydrin method and its weak interference in protein determination by the bicinchoninic acid method is easy to overcome. This surfactant exhibits a good solubilizing power toward membrane proteins, with a marked selectivity for spiralin, a bacterial surface antigen. Protein extraction started below the CMC, but was much more effective above this concentration threshold. NADH oxidase activity, ligand binding by the glycine betaine-binding protein, and antigenicity of more than 20 membrane or soluble proteins were not altered by NOGA. Thus, owing to its extraction efficacy and mildness toward protein structure and activity, NOGA should prove useful for membrane studies and offers the additional advantage of being easy to synthesize at low cost.     

Studies of the denaturation patterns of bovine alpha-crystallin using an ionic denaturant, guanidine hydrochloride and a non-ionic denaturant, urea

The effects of non-ionic and ionic denaturation and denaturation/renaturation on the native structure of alpha-crystallin at room temperature were examined. Native alpha-crystallin, at concentrations above and below the previously reported critical micelle concentration (CMC) range, was denatured by varying concentrations of urea and guanidine hydrochloride. The resulting denatured samples were examined by gel filtration fast performance liquid chromatography (FPLC), circular dichroism spectropolarimetry (CD), and transmission electron microscopy. Elution peak samples from gel filtration chromatography with sufficiently high concentrations were examined for subunit composition by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The studies presented herein demonstrate that the denaturation and renaturation of alpha-crystallin via non-ionic urea denaturation results in different renaturation species, depending upon the initial concentration of alpha-crystallin which is denatured and the concentration of urea, including certain species which, by gel filtration FPLC, have an apparent molecular weight greater than the native 800 kD aggregate. Transmission electron microscopy has also demonstrated the existence of a high molecular weight aggregate form for denatured samples. Ionic dissociation, in contrast, proceeds much in the same manner above and below the CMC range, the major difference occurring at 2 M guanidine hydrochloride. alpha B-crystallin is preferentially removed from the native alpha-crystallin aggregate upon treatment with 2 M guanidine hydrochloride indicating, once again, differences between the two subunits. Above and below the CMC range, dissociation with guanidine hydrochloride appears to plateau after 4 M guanidine hydrochloride as indicated by the presence of two apparent homotetrameric species and no further dissociation of these species with increasing guanidine hydrochloride concentrations. CD demonstrates that some secondary structure, which is lost with lower concentrations of alpha-crystallin, is still present when concentrations of alpha-crystallin, well above the critical micelle concentration range, are treated with high concentrations of urea at room temperature. In contrast, concentrations both above and below the CMC range demonstrate a significant loss of secondary structure upon treatment with 2 M guanidine hydrochloride. Finally, ionic denaturation and subsequent renaturation results in the formation of a species which is functionally incapable of protecting gamma-crystallin from heat-induced aggregation.     

Determination of surfactant critical micelle concentration by a novel fluorescence depolarization technique

A novel method using fluorescence depolarization to determine the critical micelle concentrations (CMC) of surfactants was developed. Fluorescence anisotropies of Triton X-100, sodium dodecyl sulfate, and sodium cholate were measured using 1,6-diphenyl-1,3, 5-hexatriene as a fluorescence probe. Fluorescence anisotropy decreased with increasing surfactant concentrations below the CMC and leveled off above the CMC. The depolarization method does not depend on the concentration of DPH and is largely immune to light-scattering problems encountered in turbid aqueous systems.     

Enhanced Solubility and Biodegradation of Naphthalene with Biosurfactant

Biosurfactant was produced by fermenting kerosene and used vegetable oil using a Pseudomonas sp. under nonsterile conditions. The biosurfactant at a concentration of 0.5 g∕L and pH of 10.5 lowered the surface tension of water to 25 mN∕m. The biosurfactant was used to enhance the solubility of naphthalene, and the results are compared to an anionic (sodium dedecyl sulfate) and a nonionic (Triton X-100) surfactant. The biosurfactant (5 g∕L at pH of 7) enhanced the solubility of naphthalene to more than 30 times its aqueous solubility. Solubilized naphthalene in Triton X-100 and biosurfactant solutions was biodegraded by the same microorganism that produced the biosurfactant. Naphthalene solubilized in biosurfactant and Triton X-100 (400–600 mg∕L) was biodegraded in 40 days and 100 h, respectively. Naphthalene in the amount of 30 mg∕L was degraded by the Pseudomonas sp. in 2 days. The biosurfactant was also biodegraded during the biodegradation of naphthalene, but this was not the case with Triton X-100. The biodegradation of the biosurfactant appeared to compete with the biodegradation of naphthalene. Sodium dedecyl sulfate inhibited the biodegradation of naphthalene at the conditions studied.     

Chlorinated Solvent Removal Using Food Grade Surfactants: Column Studies

In laboratory column studies we evaluated chlorinated solvent removal using food grade surfactant-based solubilization and mobilization systems. We used nonionic sorbitan polyethoxylate monostearate for solubilization experiments, and both bis-2-ethylhexyl sodium sulfosuccinate and sodium mono- and dimethyl naphthalene sulfonate in mobilization studies. Surfactant enhanced mobilization was shown to be more efficient than solubilization for removing tetrachloroethylene. Excellent removal efficiency was maintained even when the mobilization system was varied, demonstrating the robustness of this system for subsurface remediation. The selected food grade surfactants, however, suffered mass losses in the column, probably due to the occurrence of phase separations (e.g., formation of precipitates or liquid crystals). Thus, surfactant losses need to be minimized before using these systems in full-scale applications. This study also demonstrated that surfactant performance was influenced by a variety of factors, such as the type of microemulsion, temperature, and contaminant compositions, that must also be considered in design of field implementations.     

Development of novel chitosan derivatives as micellar carriers of taxol

PURPOSE: To develop an intravenous injectable carrier composed of chitosan derivatives for taxol. METHODS: A chitosan with lauryl groups attached to amino groups to provide the hydrophobic moieties and, carboxymethyl groups attached to hydroxy groups to provide the hydrophilic moieties (N-lauryl-carboxymethyl-chitosan = LCC), was newly synthesized. The solubility of taxol in LCC micelles in aqueous solution was examined. The hemolysis test of LCC and the growth inhibition experiment of taxol-loading micelle using KB cells were also performed as in vitro assay. RESULTS: It was found that LCC solubilized taxol by forming micelles with particle sizes less than 100nm. This particle size was considered effective for passive targeting for tumors. The concentration of taxol in the micellar solution was very high, with a maximum of 2.37mg/mL. This maximum was 1000 times above that in a saturated solution of taxol at pH 7.4. Hemolysis testing as an in vitro assay indicated that LCC was safer than Polysorbate 80 (TO-10M) as intravenous surfactant in terms of induction of membrane damage. As judged by cytostatic activity against KB cells, taxol retained activity even when included in LCC micelles. LCC-entrapped taxol was more effective in cytostatic activity than free taxol in low concentrations. CONCLUSIONS: The results of solubilization capacity examination, hemolysis testing, and cytostatic activity suggest that LCC may be useful as a carrier of taxol.     

Purification of the stress protein alpha B-crystallin and its differentially phosphorylated forms

The subsolubilizing alterations caused by a series of alkyl glucosides (alkyl chain lengths ranging from C8 to C12) in unilamellar phosphatidylcholine (PC) liposomes were investigated. The surfactant to phospholipid molar ratios (RE) and the normalized bilayer/aqueous phase partition coefficients (K) were determined by monitoring the increase of the fluorescence intensity of liposome suspensions due to the 5(6)-carboxyfluorescein (CF) released from the interior of vesicles to the bulk aqueous phase. Given that the free surfactant concentrations was always lower than the critical micelle concentration (CMC) of the surfactant tested we may assume that the surfactant-liposome interactions were mainly ruled by the action of surfactant monomers. In general terms, the decrease in the surfactant alkyl chain length (or the rise in the surfactant CMC) resulted in an increase in the ability of these surfactants to alter the permeability of liposomes and, inversely, in an abrupt decrease in their affinity with these bilayers structures. The overall balance of these opposite tendencies shows that at the two interaction levels studied (50 and 100% of CF release) the nonyl and the octyl glucoside showed, respectively, the highest ability to alter the release of the CF trapped in bilayers (lowest RE values), whereas the dodecyl glucoside showed the highest degree of partitioning into liposomes or affinity with these bilayer structures (highest K values).     

Structural phase transitions involved in the interaction of phospholipid bilayers with octyl glucoside

The transitional stages induced by the interaction of the nonionic surfactant octyl glucoside (OcOse) on phosphatidylcholine liposomes were studied by means of transmission electron microscopy (TEM), light scattering and permeability changes. A linear correlation was observed between the effective surfactant/lipid molar ratio (Re; three-stage model proposed for liposome solubilization) and the OcOse concentration in the initial and final interaction stages, despite showing almost a constant value during bilayer saturation. The bilayer/aqueous phase partition coefficient (K) decreased in the subsolubilizing interaction steps and increased during solubilization. Thus, whereas a preferential distribution of surfactant monomers in the aqueous phase with respect to the lipid bilayers took place in the initial interaction steps, a larger association of OcOse molecules with these lipids in bilayers occurred during solubilization. The initial steps of bilayer saturation (50-70% permeability) were attained for a lower free surfactant (Sw) than that for its critical micellar concentration (cmc). When Sw reached the OcOse cmc, solubilization started to occur (Resat). Large unilamellar vesicles began to form as the OcOse exceeded 60 mol/100 mol, exhibiting for 65 mol/100 mol (50% permeability) vesicles of approximately 400 nm. TEM pictures for 100% permeability (72 mol/100 mol) and Resat still showed unilamellar vesicles, albeit that the Resat TEM picture showing traces of smaller structures. Exceeding surfactant amounts led to a decrease in static light scattering; the vesicle-size curve began to show a bimodal distribution. The TEM picture showed tubular structures together with bilayer fragments. Thereafter, the open structures were gradually affected by the surfactant and the scattered intensity gradually decreased to a constant low value.     

Effects of preservation methods, parasites, and gut contents of black flies (Diptera: Simuliidae) on polymerase chain reaction products

The vesicle to micelle transition which results in the interaction of the Triton X-100 surfactant with phosphatidylcholine vesicles was studied by means of dynamic light scattering (at different reading angles) and by freeze-fracture electron microscopy techniques. Vesicle solubilization was produced by the direct formation of mixed micelles without the formation of complex intermediate aggregates. Thus, vesicle to micelle transformation was mainly governed by the progressive formation of mixed micelles within the bilayer. A subsequent separation of these micelles from the liposome surface (vesicle perforation by the formation of surfactant-stabilized holes on the vesicle surface) led to a complete solubilization of liposomes.     

Fluorimetric and solubility studies of nadolol and atenolol in SDS micelles

The effect of sodium dodecyl sulfate (SDS) micelles on the spectrofluorimetric intensities and on the solubility of two beta-blockers (atenolol and nadolol) were studied at 25.0 +/- 0.1 degrees C and I = 0.1 M NaCl. From the dependence of these physical properties on SDS concentration it was possible to calculate the binding constants drug-micelle, and it was found that both techniques yield similar results for the binding constants, and that are in agreement with those calculated from the effect of micelles on the apparent acidity constants of the beta-blockers.     

Electrochemical Desulfurization of Waste Gases in a Batch Reactor

To meet the increasing need for reduction of exhaust emissions from stationary sources, many technologies have been developed to remove SO2 from flue gas. In this study the anodic oxidation of sulfur dioxide in aqueous solutions of sulfuric acid with a unique reactor design and electrode configuration has been investigated. An electrochemical absorption column larger than laboratory scale was employed. A titanium rod cathode and platinum expanded mesh anode separated by a cation exchange membrane were used as electrodes in the cylindrical electrochemical reactor. The effects of current densities of 10, 1, and 0.1?Am?2, initial SO2 concentrations of 500, 2,500, and 5,000?ppm, gas flow rates of 0.75, 1.5, and 5?L min?1, sulfuric acid concentrations of 1, 5, and 10%(w), gas composition, and electrolysis time on removal efficiency, current efficiency, energy consumption, and mass transfer coefficient were reported. Removal efficiency of 94% was obtained with a high current efficiency of 94%, energy consumption of 2.22×10?2?kW?hm?3, and mass transfer coefficient of 5.9×10?5?ms?1 without additives or pretreatment. At the current densities of 0.1, 1, and 10?Am?2, the removal efficiencies were 10, 94, and 98%, respectively. Removal efficiency was observed to decrease as inlet SO2 concentration, gas flow rate, and electrolyte concentration increased. The presence of CO2 in the gas mixture led to a decrease in the SO2 removal efficiency. During electrochemical absorption of SO2 into the H2SO4 solution, the concentration of acid is increased from 5 to 10%. At the end of the studies, electrochemical desulfurization succeeded in meeting the regulation requirement, and the absorbing liquid remained in a reusable form.     

湿法炼锌铁钒除铁工艺管路结晶的机理探讨

通过对湿法炼锌过程所涉及的三元体系M_2SO_4-ZnSO_4-H_2O(M=K,Na,NH4)溶解度相图的比较研究,发现在上述三元体系中,在一般的冶炼工艺条件下,复盐(如(NH_4)_2SO_4·ZnSO_4·6H_2O(s)、Na_2SO_4·ZnSO_4·4H_2O(s)、K_2SO_4·ZnSO_4·6H_2O(s)远比单盐(如ZnSO_4·7H_2O(s)、Na_2SO_4(s)、K_2SO_4(s))要容易析出得多。这些复盐在溶液中的溶解度均随着温度的降低而降低,是管路结晶的主要诱因。溶解度较小的((NH_4)_2SO_4·ZnSO_4·6H_2O(s)生成是导致黄铵铁钒除铁过程管路易结晶堵塞的主因。     

Organo-Illite as a Low Permeability Sorbent to Retard Migration of Anionic Contaminants

Landfill leachate, often having high concentrations of metal cations, anions, and organic compounds, presents a great threat to nearby groundwater. Due to negative charges on soil particles, regular clay liners cannot effectively retard the movement of anionic contaminants such as chromate. In this paper, a natural illite was modified by cationic surfactants with different chain lengths and tested for its chromate removal efficiency. When the surfactant tail group is relatively short and the solution critical micelle concentration is high, the sorbed surfactant molecules form a monolayer on illite, resulting no chromate sorption by the organo-illite. As the chain length of surfactant tail group increases, the critical micelle concentration reduces and the surfactant molecules sorb as admicelles on illite with the surfactant sorption exceeding the illite’s cation-exchange capacity. Such admicelle modification makes the organoclay capable of retaining chromate instantaneously and retarding the movement of chromate by 1–2 orders of magnitude. The illite’s hydraulic conductivity showed a slight increase after surfactant modification, from 1×10?7 to 8×10?7?cm/s, probably due to reduced packing density after modification. Chromate breakthrough data from column transport experiments were well described by a one-dimensional advection-dispersion model that incorporated Langmuir sorption.     

The inhibitory effect of carboxymethylcellulose with high viscosity on lipid absorption in broiler chickens coincides with reduced bile salt concentration and raised microbial numbers in the small intestine

Two diets, with or without a nonfermentable carboxymethylcellulose (CMC) with high viscosity, were fed to broiler chickens beginning at 2 wk of age to study whether the anti-nutritive effect of gelling fibers on lipid digestibility may be associated with reduced intestinal bile salt concentration. Moreover, the microflora were examined to study whether possible changes in bile salt concentration coincide with alterations in microbial numbers. Carboxymethylcellulose depressed apparent lipid digestibility (P = 0.021). Feed intake and weight gain were not significantly affected. Water intake was increased in birds fed the CMC diet (P = 0.039). Bile acid concentration in small intestinal digesta was decreased (P = 0.047) in birds fed the CMC diet, which may have been caused by the increased water content of digesta (P < 0.001). The concentration of bile acids per gram dry matter or per milligram chromium was not reduced in small intestinal contents. Broiler chickens fed the CMC diet excreted more bile acids in the excreta (P < 0.001). Total aerobic and anaerobic microbial counts in the intestinal digesta were significantly increased in the duodenum plus jejunum (P = 0.038) but not in the ileum. Significant increases were found in the numbers of Clostridia (P = 0.017), Lactobacillus (P = 0.009), Bacteroides (P = 0.022), and yeasts and molds (P = 0.012). The present study supports the hypothesis that a nonfermentable gelling fiber (CMC) decreases apparent lipid digestibility by reducing the concentration of bile acids in the chyme in broiler chickens. Moreover, the ingestion of gelling fibers may increase the bacterial activity in the small intestine, which may further contribute to malabsorption of lipids.     

Growth of a turbidostat culture of yeasts in the presence of a high concentration of compounds in a stationary mode and under osmotic shock conditions

The growth of a turbidostat culture of the yeast strain Saccharomyces cerevisiae 14 was studied under steady-state conditions in the presence of high (1.2-3 M) concentrations of various soluble compounds and under transition conditions upon rapid concentration changes. The concentration was varied from the optimal one to that decreasing the growth rate two times and back to the optimal one. The effects of the following compounds on yeast growth in the steady-state regime were studied: glucose, sucrose, (NH4)2SO4, MgSO4, NaH2PO4, Na2SO4, KCl, NaCl, NH4Cl, MgCl2, and LiCl. To study transition processes, the following compounds were used: NH4Cl, NaH2PO4, MgCl2, MgSO4, (NH4)2SO4, KCl, and NaCl. When the NaCl concentration increased rapidly, the transition process was completed in the first generation. For the other compounds, this process lasted for several generations. The transition process was completed in the first generation in cultures previously inhibited by (NH4)2SO4 or NaH2PO4. Cell volume varied insignificantly among steady-state cultures grown under different conditions, except for those inhibited by NH4Cl or MgSO4. The level of glucose utilization increased with an increase in the concentrations of the compounds studied. The ratio of the duration of the juvenile developmental phases (prophase, metaphase) to the duration of the postjuvenile phases (anaphase, telophase) was constant over the concentration ranges tested. The inhibitory effect of a compound depended on its chemical nature rather than on its osmotic effect.     

The association of different detergents with the photosynthetic reaction center protein of Rhodobacter sphaeroides R26 and the effects on its photochemistry

Detergent-free reaction centers from Rhodobacter sphaeroides R26 were used to study the solubilization of reaction centers in various detergents and their effects on reaction center photochemistry. 500 +/- 100 n-octyl-beta-D-glucopyranoside or 51 +/- 5 Triton X-100 molecules were associated with one reaction center. For N.N-alkylamine N-oxide detergents with chain lengths in the range from 8-13 carbon atoms, the number of detergent molecules associated with the reaction centers increased with decreasing chain length. The amount of detergent molecules associated with the reaction centers decreased almost tenfold if the pH was increased from pH 6 to pH 10. The addition of 5% 1,2,3-heptanetriol to various detergents lowered the detergent/reaction center ratio by a factor of two compared to that for the pure detergent. The detergent concentration at which solubilization of the reaction center occurs was close to the critical micelle concentration for all detergents studied. The absorption band at 865 nm of the primary donor in the reaction center shifts to 846 nm when detergent was removed from the reaction center; upon resolubilization with various detergents, this band shifts back to 865 nm. In 80-90% of the detergent-free reaction centers, the secondary electron transfer from QA to QB was inhibited: this electron transfer was restored after re-addition of detergent.