Correlation of membrane/water partition coefficients of detergents with the critical micelle concentration

The membrane/water partition coefficients, K, of 15 electrically neutral (non-charged or zwitterionic) detergents were measured with phospholipid vesicles by using isothermal titration calorimetry, and were compared to the corresponding critical micellar concentrations, cmc. The detergents measured were oligo(ethylene oxide) alkyl ethers (C(m)EO(n) with m = 10/n = 3, 7 and m = 12/n = 3.8); alkylglucosides (octyl, decyl); alkylmaltosides (octyl, decyl, dodecyl); diheptanoylphosphatidylcholine; Tritons (X-100, X-114) and CHAPS. A linear relation between the free energies of partitioning into the membrane and micelle formation was found such that K. CMC approximately 1. The identity K. CMC = 1 was used to classify detergents with respect to their membrane disruption potency. "Strong" detergents are characterized by K. CMC < 1 and solubilize lipid membranes at detergent-to-lipid ratios X(b) < 1 (alkylmaltosides, tritons, heptaethylene glycol alkyl ethers). "Weak" detergents are characterized by K. CMC > 1 and accumulate in the membrane- to detergent-to-lipid ratios X(b) > 1 before the bilayer disintegrates (alkylglucosides, pentaethylene glycol dodecyl ether).     

Novel redox surfactants and their interactions with glucose oxidase of Aspergillus niger

A number of novel redox surfactants (based on mixed bipyridine/dipyridylamine complexes of osmium (II) where the dipyridylamine ligands bears a saturated C(8), C(10), C(12), C(14), or C(16) alkyl chain) were synthesized and characterized electrochemically and biochemically as mediators for glucose oxidase (EC 1.1.3.4, GOD) of Aspergillus niger. These compounds exhibited critical micelle concentrations (CMCs) in phosphate-buffered saline solution (pH 7.4) in the range 10(-4) 10 10(-3) M, the value decreasing with increasing chain length. Dependence of a number of properties (speed of mediation, redox potential, denaturing action on the enzyme, adsorption on an electrode surface) on the length of the mediator alkyl chain was observed. The presence of an alkyl chain decreased the rate of mediation relative to otherwise similar nonsurfactant mediators, and the longer alkyl chain, the slower the rate of mediation. For each compound, mediation above the CMC was about tenfold slower than that observed below the CMC. However, for the cases of mediator absorbed on an electrode surface with GOD, longer chains give increased physisorption of mixed micelles of enzyme and mediator. The compounds were incidentally found to inhibit the glucose oxidase activity of GOD in a complex manner; inhibition increased with increasing chain length and the deactivation, for any given compound, was more pronounced below the CMC than above. Glucose oxidase activity assays and study of the action of surfactants and mediators on the fluorescent properties of carboxy-fluorescein-labeled GOD led to the consideration of a model for redox surfactant-GOD interaction where three mechanisms may operate: first, a selective interaction of mediators with the GOD active site; second, a nondenaturing association of short-chain (相似文献   

Hydrophobic thickness, lipid surface area and polar region hydration in monounsaturated diacylphosphatidylcholine bilayers: SANS study of effects of cholesterol and beta-sitosterol in unilamellar vesicles

The influence of a mammalian sterol cholesterol and a plant sterol beta-sitosterol on the structural parameters and hydration of bilayers in unilamellar vesicles made of monounsaturated diacylphosphatidylcholines (diCn:1PC, n=14-22 is the even number of acyl chain carbons) was studied at 30 degrees C using small-angle neutron scattering (SANS). Recently published advanced model of lipid bilayer as a three-strip structure was used with a triangular shape of polar head group probability distribution (Kucerka et al., Models to analyze small-angle neutron scattering from unilamellar lipid vesicles, Physical Review E 69 (2004) Art. No. 051903). It was found that 33 mol% of both sterols increased the thickness of diCn:1PC bilayers with n=18-22 similarly. beta-sitosterol increased the thickness of diC14:1PC and diC16:1PC bilayers a little more than cholesterol. Both sterols increased the surface area per unit cell by cca 12 A(2) and the number of water molecules located in the head group region by cca 4 molecules, irrespective to the acyl chain length of diCn:1PC. The structural difference in the side chain between cholesterol and beta-sitosterol plays a negligible role in influencing the structural parameters of bilayers studied.     

New structural model for mixed-chain phosphatidylcholine bilayers

Multilamellar suspensions of a mixed-chain saturated phosphatidylcholine with 18 carbon atoms in the sn-1 chain and 10 carbon atoms in the sn-2 chain have been analyzed by X-ray diffraction techniques. The structural parameters for this lipid in the gel state are quite different than usual phosphatidylcholine bilayer phases. A symmetric and sharp wide-angle reflection at 4.11 A indicates that the hydrocarbon chains in hydrated C(18):C(10)PC bilayers are more tightly packed than in usual gel-state phosphatidylcholine bilayers and that there is no hydrocarbon chain tilt. The lipid thickness is about 12 A smaller than would be expected in a normal bilayer phase, and the area per molecule is 3 times the area per hydrocarbon chain. In addition, the bilayer thickness increases upon melting to the liquid-crystalline state, whereas normal bilayer phases decrease in thickness upon melting. On the basis of these data, we propose a new lipid packing model for gel-state C(18):C(10)PC bilayers in which the long C(18) chain spans the entire width of the hydrocarbon region of the bilayer and the short C(10) chain aligns or abuts with the C(10) chain from the apposing molecule. This model is novel in that there are three hydrocarbon chains per head group at the lipid-water interface. Calculations show that this phase is energetically favorable for mixed-chain lipids provided the long acyl chain is nearly twice the length of the shorter chain. In the liquid-crystalline state C(18):C(10)PC forms a normal fluid bilayer, with two chains per head group.(ABSTRACT TRUNCATED AT 250 WORDS)     

Solubilization of human erythrocyte membranes by non-ionic surfactants of the polyoxyethylene alkyl ethers series

In the present study, we investigated the interaction of the non-ionic surfactants polyoxyethylene alkyl ethers (C(n)E(m)) with erythrocyte membranes. For this purpose we have performed hemolytic assays under isosmotic conditions with five surfactants in the 8 polyoxyethylene ether series. By applying to the hemolytic curves a quantitative treatment developed for the study of surface-active compounds on biomembranes, we could calculate the surfactant/lipid molar ratios for the onset of hemolysis (R(e)(sat)) and for complete hemolysis (R(e)(sol)). This approach also allowed the calculation of the binding constants for each surfactant to the erythrocyte membrane. Results in the C(n)E(m) series were compared to those obtained for Triton X-100, a well-known non-ionic surfactant with values of cmc and HLB in the range of the alkyl ethers studied. Inside the series the lytic effect increased with the more hydrophobic homologues (C(10)E(8)相似文献   

Effect of protein-surfactant interactions on aggregation of β-lactoglobulin

The milk protein β-lactoglobulin (βLG) dominates the properties of whey aggregates in food products. Here we use spectroscopic and calorimetric techniques to elucidate how anionic, cationic and non-ionic surfactants interact with bovine βLG and modulate its heat-induced aggregation. Alkyl trimethyl ammonium chlorides (xTAC) strongly promote aggregation, while sodium alkyl sulfates (SxS) and alkyl maltopyranosides (xM) reduce aggregation. Sodium dodecyl sulfate (SDS) binds to non-aggregated βLG in several steps, but reduction of aggregation was associated with the first binding step, which occurs far below the critical micelle concentration. In contrast, micellar concentrations of xMs are required to reduce aggregation. The ranking order for reduction of aggregation (normalized to their tendency to self-associate) was C10-C12>C8>C14 for SxS and C8>C10>C12>C14>C16 for xM. xTAC promote aggregation in the same ranking order as xM reduce it. We conclude that SxS reduce aggregation by stabilizing the protein's ligand-bound state (the melting temperature t(m) increases by up to 10°C) and altering its charge potential. xM monomers also stabilize the protein's ligand-bound state (increasing t(m) up to 6°C) but in the absence of charged head groups this is not sufficient by itself to prevent aggregation. Although micelles of both anionic and non-ionic surfactants destabilize βLG, they also solubilize unfolded protein monomers, leaving them unavailable for protein-protein association and thus inhibiting aggregation. Cationic surfactants promote aggregation by a combination of destabilization and charge neutralization. The food compatible surfactant sodium dodecanoate also inhibited aggregation well below the cmc, suggesting that surfactants may be a practical way to modulate whey protein properties.     

Influence of N-dodecyl-N,N-dimethylamine N-oxide on the activity of sarcoplasmic reticulum Ca(2+)-transporting ATPase reconstituted into diacylphosphatidylcholine vesicles: efects of bilayer physical parameters

Sarcoplasmic reticulum Ca-transporting ATPase (EC 3.6.1.38) was isolated from rabbit white muscle, purified and reconstituted into vesicles of synthetic diacylphosphatidylcholines with monounsaturated acyl chains using the cholate dilution method. In fluid bilayers at 37 degrees C, the specific activity of ATPase displays a maximum (31.5+/-0.8 IU/mg) for dioleoylphosphatidylcholine (diC18:1PC) and decreases progressively for both shorter and longer acyl chain lengths. Besides the hydrophobic mismatch between protein and lipid bilayer, changes in the bilayer hydration and lateral interactions detected by small angle neutron scattering (SANS) can contribute to this acyl chain length dependence. When reconstituted into dierucoylphosphatidylcholine (diC22:1PC), the zwitterionic surfactant N-dodecyl-N,N-dimethylamine N-oxide (C12NO) stimulates the ATPase activity from 14.2+/-0.6 to 32.5+/-0.8 IU/mg in the range of molar ratios C12NO:diC22:1PC=0/1.2. In dilauroylphosphatidylcholines (diC12:0PC) and diC18:1PC, the effect of C12NO is twofold-the ATPase activity is stimulated at low and inhibited at high C12NO concentrations. In diC18:1PC, it is observed an increase of activity induced by C12NO in the range of molar ratios C12NO:diC18:1PC< or =1.3 in bilayers, where the bilayer thickness estimated by SANS decreases by 0.4+/-0.1 nm. In this range, the 31P-NMR chemical shift anisotropy increases indicating an effect of C12NO on the orientation of the phosphatidylcholine dipole N(+)-P- accompanied by a variation of the local membrane dipole potential. A decrease of the ATPase activity is observed in the range of molar ratios C12NO:diC18:1PC=1.3/2.5, where mixed tubular micelles are detected by SANS in C12NO+diC18:1PC mixtures. It is concluded that besides hydrophobic thickness changes, the changes in dipole potential and curvature frustration of the bilayer could contribute as well to C12NO effects on Ca(2+)-ATPase activity.     

Dynamics of lipid chain attached fluorophore 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) in negatively charged membranes determined by NMR spectroscopy

We have determined the average location and dynamic reorientation of the fluorophore 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) attached to a C12 sn-2 chain of a phosphatidylserine (PS) analogue (C12-NBD-PS) in zwitterionic phosphatidylcholine (PC) and negatively charged phosphatidylserine (PS) host membranes. (1)H magic angle spinning nuclear Overhauser enhancement spectroscopy indicates a highly dynamic reorientation of the aromatic molecule in the membrane. The average location of NBD is characterized by a broad distribution function along the membrane director with a maximum indicating the location of the probe in the lipid/water interface of the lipid membrane. This behavior can be explained by a backfolding of the sn-2 chain towards the aqueous phase. Small differences in the distribution profiles of the NBD group along the membrane normal between PC and PS host membranes were found: in a PC host membrane, the NBD distribution has its maximum in the glycerol region; in a PS host membrane, NBD resides mostly in the upper chain region. These differences may be accounted for by packing differences in the PC versus PS host membranes. As seen by (2)H NMR order parameters, PS bilayers show a much higher packing density compared to PC membranes. Consequently, backfolding of the sn-2 chain with the NBD group attached causes a larger decrease of molecular order of the sn-1 chain in PS than in PC membranes. The broad distributions obtained for lipid chain attached NBD molecules reflect the motional freedom and molecular disorder in the liquid-crystalline lipid membrane.     

Effect of lipid acyl chain length on activity of sodium-dependent leucine transport system in Pseudomonas aeruginosa

The sodium-dependent leucine transport system of Pseudomonas aeruginosa was reconstituted into liposomes of binary lipid mixtures of dilauroylphosphatidylethanolamine (di(12:0)PE)/phosphatidylcholine (PC) with cis-monounsaturated fatty acid chains (di(n:1)PC) (n = 14-22) or dioleoylphosphatidylethanolamine (di(18:1)PE)/di(n:1)PC (n = 14-22). Leucine carrier proteins can be activated with phosphatidylethanolamine, whereas activation does not occur in PC-reconstituted vesicles (Uratani, Y., and Aiyama, A. (1986) J. Biol. Chem. 261, 5450-5454). Na+-dependent counterflow was measured at 30 degrees C as reconstituted transport activity. Proteoliposomes containing di(12:0)PE exhibited high counterflow activity at the PC acyl carbon number (n) of 18 and 20 but no or low activity at n = 14, 16, and 22. On the other hand, proteoliposomes containing di(18:1)PE exhibited higher transport activity than those vesicles with di(12:0)PE and corresponding di(n:1)PC. A lipid mixture of di(18:1)PE and di(16:1)PC supported maximal activity. These results show that the leucine transport system of P. aeruginosa is dependent on the lipid acyl chain length and suggest that there exists optimal bilayer thickness for maximal carrier activity.     

Potential therapeutic antioxidants that combine the radical scavenging ability of myricetin and the lipophilic chain of vitamin E to effectively inhibit microsomal lipid peroxidation

The flavonol myricetin, reacts with oxygen-centred galvinoxyl radicals 28 times faster than d-alpha-tocopherol (vitamin E), the main lipid-soluble antioxidant in biological membranes. Moreover, each myricetin molecule reduces twice as many such radicals as vitamin E. However, myricetin fails to protect vitamin E-deficient microsomes from lipid peroxidation as assessed by the formation of thiobarbituric acid reactive substances (TBARS). Novel and potentially therapeutic antioxidants have been prepared that combine the radical-scavenging ability of a myricetin-like head group with a lipophilic chain similar to that of vitamin E. C(6)-C(12) alkyl chains are attached to the A-ring of either a 3,3',4',5'-tetrahydroxyflavone or a 3,2',4',5'-tetrahydroxyflavone head group to give lipophilic flavonoids (C log P = 4 to 10) that markedly inhibit iron-ADP catalysed oxidation of microsomal preparations. Orientation of the head group as well as total lipophilicity are important determinants of antioxidant efficacy. MM2 models indicate that our best straight chain 7-alkylflavonoids embed to the same depth in the membrane as vitamin E. The flavonoid head groups are prepared by aldol condensation followed by Algar-Flynn-Oyamada (AFO) oxidation or by Baker-Venkataraman rearrangement. The alkyl tails are introduced by Suzuki or Negishi palladium-catalysed cross-coupling or by cross-metathesis catalysed by first generation Grubbs catalyst, which tolerate phenolic hydroxyl and ketone groups.     

N1N8-bis(gamma-glutamyl)spermidine cross-linking in epidermal-cell envelopes. Comparison of cross-link levels in normal and psoriatic cell envelopes.

In order to explore the effect of electric charge on detergent solubilization of phospholipid bilayers, the interaction of nine electrically charged surfactants with neutral or electrically charged liposomes has been examined. The detergents belonged to the alkyl pyridinium, alkyl trimethylammonium or alkyl sulphate families. Large unilamellar liposomes formed by egg phosphatidylcholine plus or minus stearylamine or dicetyl phosphate were used. Solubilization was assessed as a decrease in light-scattering of the liposome suspensions. The results suggest that electrostatic forces do not play a significant role in the formation of mixed micelles and that hydrophobic interactions are by far the main forces involved in solubilization. In addition, from the study of thirty different liposome-surfactant systems, we have derived a series of empirical rules that may be useful in predicting the behaviour of untested surfactants: (i) the detergent concentration producing the onset of solubilization (Don) decreases as the alkyl chain length increases; the decrease follows a semi-logarithmic pattern in the case of alkyl pyridinium compounds; (ii) for surfactants with critical micellar concentrations (cmc) less than 6 x 10(-3) M, Don. is independent of the nature of the detergent and the bilayer composition; for detergents having cmc greater than 6 x 10(-3) M, Don. increases linearly with the cmc; and (iii) Don. varies linearly with the surfactant concentration that produces maximum solubilization.     

The lysis of isolated fish (Oncorhynchus mykiss) gill epithelial cells by surfactants

1. The interaction of a wide range of surfactants with isolated gill epithelial cells of rainbow trout (Oncorhynchus mykiss) was investigated as a function of the surfactant concentration up to and above the critical micelle concentration (cmc). The surfactants included a homologous series of n-alkyl sulphates, single and double chain tri and dimethylammonium bromides (TABs and DABs), cholates and the nonionics n-octylglucoside and Triton X-100.2. With the exception of the C₂₂ alkyl chain TAB and the double chain [(C₁₂)₂] DAB, the surfactants solubilized between 84 and 100% of the cell protein at high concentrations (>cmc).3. At low concentrations n-dodecyltrimethylammonium bromide and, to a lesser extent, Triton X-100 and sodium n-dodecylsulphate release a larger proportion of cell protein than they solubilize lipid in contrast to sodium cholate which initially preferentially solubilizes cell lipid. This differential pattern of solubilization is similar to that observed for other plasma membranes such as those of human erythrocytes and platelets.4. The surfactant concentration required to solubilize 50% (S_50%) of cell protein increases with the cmc. There is an approximately linear relationship between log(S_50%) and log cmc.5. Light microscopy shows that the surfactants at high concentrations (>cmc) fragment the secondary lamellae of the gill filaments.     

Interaction of alpha-amylase with n-alkylammonium bromides

The interaction of alpha-amylase with n-alkylammonium bromides above and below their critical micellar concentrations (cmc) has been studied in buffer at pH 7 and 10 by UV spectrophotometry, photon correlation spectroscopy and Doppler microelectrophoresis. This interaction produces a complex that is dependent on pH of the medium. This complex appears at surfactant concentrations below the cmc, which means that individual surfactant molecules can bind tightly to native alpha-amylase. The complex maintains its aggregation state when the concentration of surfactants with a hydrocarbon chain of 16 carbons increases, but not for surfactants of 12 and 14 carbons. Measurements of zeta-potential indicate the influence of electrostatic and hydrophobic forces. When the size of the aggregate is maximal, proteins are at their point of zero charge. In such conditions, Van der Waals forces and contacts between the alkyl chain and the hydrophobic core of the protein favour the formation of a larger aggregate.     

The effect of chain length on the melting temperature and size of dialkyldimethylammonium bromide vesicles

Differential scanning calorimetry (DSC) and dynamic light scattering (DLS) were used to obtain the gel to liquid-crystalline phase transition temperature (Tm) and the apparent hydrodynamic radius (Rh) of spontaneously formed cationic vesicles of dialkyldimethylammonium bromide salts (CnH2n+1)2(CH3)2N+.Br-, with varying chain lengths. The preparation of cationic vesicles from aqueous solution of these surfactants, for n=12, 14, 16 and 18 (DDAB, DTDAB, DHDAB and DODAB, respectively), requires the knowledge of the surfactant gel to liquid-crystalline phase transition temperature, or melting temperature (Tm) since below this temperature these surfactants are poorly or not soluble in water. That series of cationic surfactants has been widely investigated as vesicle-forming surfactants, although C12 and C18, DDAB and DODAB are by far the most investigated from this series. The dependence of Tm of these surfactants on the number n of carbons in the surfactant tails is reported. The Tm obtained by DSC increases non-linearly with n, and the vesicle apparent radius Rh is about the same for DHDAB and DODAB, but much smaller for DDAB.     

Controlled template-assisted assembly of plasmid DNA into nanometric particles with high DNA concentration

A series of novel cationic detergents that contain cleavable hydrophilic isothiuronium headgroups was synthesized, and their utility in controlled assembly of plasmid DNA into small stable particles with high DNA concentration investigated. The detergents have alkyl chains of C(8)-C(12) and contain hydrophilic isothiuronium headgroups that give relatively high critical micelle concentration (CMC) to the detergents (>10 mM). The isothiuronium group masks a sulfhydryl group on the detergent and can be cleaved in a controlled manner under basic conditions to generate a reactive thiol group. The thiol group can undergo a further reaction after the detergents have accumulated on a DNA template to form a disulfide-linked lipid containing two alkyl chains. The pH-dependent kinetics of cleavage of the isothiuronium group, the CMC of the surfactants, the formation of the complexes, and the transfection efficiency of the DNA complexes have been investigated. Using the C(12) detergent, a approximately 6 kilo-basepair plasmid DNA was compacted into a small particle with an average diameter of around 40 nm with a approximately -13 mV zeta-potential at high DNA concentration (up to 0.3 mg/mL). The compounds were well tolerated in cell culture and showed no cytotoxicity under their CMCs. Under appropriate conditions, the small particle retained transfection activity.     

Surfactant-induced refolding of lysozyme

The surfactant-lysozyme interaction was investigated by circular dichroism, fluorescence, UV, dynamic light scattering, surface tension, turbidity measurements and lysozyme activity assay. A new way of refolding of lysozyme was found. It was shown that the lysozyme unfolded by anionic surfactants could be renatured by adding cationic surfactants. That is, lysozyme formed precipitate with anionic surfactants, the precipitates could be dissolved by adding a cationic surfactant solution, and then the lysozyme was refolded to its native state spontaneously. Different couples of anionic surfactants and cationic surfactants including C10SO3/C10NE, C12SO3/C10NE, C10SO3/C12NE, C10SO3/C12NB, C10SO4/C10NE and C12SO4/C10NE (C(n)SO3, C(n)SO4, C(n)NE and C(n)NB represent sodium alkyl sulfonate/sulfate, alkyl triethyl/butyl ammonium bromide respectively) were investigated, all of them gave similar results. The results were explained in terms of the differences between the interaction of anionic-cationic surfactants and that of surfactant-lysozyme. It was thought that the formation of mixed micelles of anionic-cationic surfactants is a more favorable process than that of lysozyme-surfactant complexes, which induces the dissociation of lysozyme-surfactant complexes when cationic surfactants were added.     

The influence of the polar head and the hydrophobic chain on the skin penetration enhancement effect of poly(ethylene glycol) derivatives

The effect of a homologue series of nonionic surfactants, namely poly(ethylene glycol) (PEG) fatty acid esters, differing in oxyethylene (PEG 8, PEG 12, and PEG 40) and fatty acid (stearate, mono and di-laurate, and mono and di-oleate) chain lengths, on in vitro skin permeability of ketoprofen (KTP) vehicled in plasters was investigated. The drug diffusion through hairless mouse skin as well as the effect of the surfactant type and strength was studied by Franz diffusion cells and ATR-FTIR spectroscopy. The use of PEG stearate series revealed that the surfactant with the largest polar head, namely PEG 40, was ineffective in enhancing the skin permeation of KTP, independently of the plaster concentrations. The effect of the hydrophobic chain was investigated only by using the shortest oxyethylene chains. The experimental results revealed that the oxyethylene chain length of surfactants appeared to be more influent than the alkyl chain. The prediction of the absorption enhancing capability of these PEG derivatives appeared related to the vehicle other than the proper combination of the number of ethylene oxide groups and alkyl groups.     

Synthesis and characterisation of new types of side chain cholesteryl polymers

A series of cholesterol derivatives have been synthesised via the alkylation reaction of the 3-hydroxyl group with the aliphatic bromide compounds with different chain lengths, namely 3β-alkyloxy-cholesterol. The double bond between the C5 and C6 positions in these cholesterol derivatives was oxidised into epoxy, followed by an epoxy-ring-opening reaction with the treatment with acrylic acid, resulting in a series of 3β-alkyloxy-5α-hydroxy-6β-acryloyloxycholesterol, C(n)OCh (n=1, 2, 4, 6, 8, 10, 12), The acrylate group is connected to the C6 position, which is confirmed by the single crystal structure analysis. The corresponding polymers, PC(n)OCh, were prepared via free radical polymerisation. The structure of monomers and the resulting polymers were characterised with nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR) and gel permeation chromatography (GPC). The thermal properties of PC(n)OCh were studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). To determine the secondary structure of polymers, circular dichroism (CD) spectra were performed. It was found that not all monomers produce high-molecular-weight polymers because of steric hindrance. However, all polymers have a helical structure, which can be enhanced by increasing the alkoxy chain length. In addition, increasing the alkoxy chain length decreases the glass transition temperature and increases the decomposition temperature of the polymers.     

Gentisides C–K: Nine new neuritogenic compounds from the traditional Chinese medicine Gentiana rigescens Franch

Nine new alkyl 2,3-dihydroxybenzoates, gentisides C–K, were isolated from the traditional Chinese medicine Gentiana rigescens Franch. Their structures and stereochemistry were elucidated by spectroscopic methods, and comparison of the specific rotation with that of the gentiside B. These metabolites are additional members of the gentisides which belong to a novel class of neuritogenic compounds. They are structurally different from one another because they possess varying alkyl chain lengths, with or without an isobutyl or isopropyl group at the end of the alkyl chain. These compounds are potent inducers of neurite outgrowth on PC12 cells. The gentiside C possessing the shortest alkyl chain length exhibited the highest neuritogenic activity among all of the gentisides. Gentiside C showed a significant neuritogenic activity at 1 μM against PC12 cells comparable to that seen for the best nerve growth factor (NGF) concentration of 40 ng/mL. In addition, evident neuritogenic activity was observed in the cells when treated with gentiside C at a concentration as low as 0.03 μM. The structure–activity relationships within the gentisides A–K revealed that alkyl chain length is important for the activity, but structure diversity at the end of the alkyl chain is not.     

Effects of nonionic surfactants on the solubilization and mineralization of phenanthrene in soil-water systems

The solubilization and mineralization of (14)C-phenanthrene in soil-water systems was examined with several commercially available surface-active agents, viz., an alkyl ethoxylate C(12)E(4); two alkylphenol ethoxylate surfactants: C(8)PE(9.5) and C(9)PE(10.5); two sorbitan ethoxylate surfactants: the sorbitan monolaurate (Tween 20) and the sorbitan monooleate (Tween 80); two pairs of nonionic ethoxylate surfactant mixtures: C(12)E(4)/C(12)E(23) at a 1:1 ratio, and C(12-15)E(3)/C(12-15)E(9) at a 1:3 ratio; and two surfactants possessing relatively high critical micelle concentration (CMC) values and low aggregation numbers: CHAPS and octyglucoside. Surface tension experiments were performed to evaluate surfactant sorption onto soil and the surfactant doses required to attain the CMC in the soil-water systems. Surfactant solubilization of (14)C-phenanthrene commenced with the onset of micellization. The addition of surface-active agents was observed not to be beneficial to the microbial mineralization of phenanthrene in the soil-water systems and, for supra-CMC surfactant doses, phenanthrene mineralization was completely inhibited for all the surfactants tested. A comparison of solubilization, surface tension, and mineralization data confirms that the inhibitory effect on microbial degradation of phenanthrene is related to the CMC of the surfactant in the presence of soil. Additional tests demonstrated the recovery of mineralization upon dilution of surfactant concentration to sub-CMC levels, and a relatively high exit rate for phenanthrene from micelles. These tests suggest that the inhibitory effect is probably related to a reversible physiological surfactant micelle-bacteria interaction, possibly through partial complexing or release of membrane material with disrupting membrane lamellar structure. This study indicates that nonionic surfactant solubilization of sorbed hydrophobic organic compounds from soil may not be beneficial for the concomitant enhancement of soil bioremediation. Additional work is needed to address physicochemical processes for bioavailability enhancement, and effects of solubilizing agents on microorganisms for remediation and treatment of hydrophobic organic compounds and nonaqueous phase liquids. (c) 1992 John Wiley & Sons Inc.