Antiviral activity and active components of the leaves from Sabia parviflora Wall. ex Roxb.

Sabia parviflora (SP, "xiao hua qing feng teng" in Chinese) was recorded as an important ethnic medicine to be used for treating viral hepatitis. The antiviral activity of four SP extracts and potent antiviral compounds evaluated with cathepsin L protease (Cat L PR) and HIV-1 protease (HIV-1 PR). UPLC-HRMS was used for identifying the bioactive components. In addition, the possible inhibitory mechanism of the identified compounds on viral protease was further discussed by molecular docking. As a result, four extracts of SP exhibited inhibitory activity of HIV-1 PR and Cat L PR with IC50 range from 0.015 to 0.80 mg/mL. Meanwhile, six compounds inhibited HIV-1 PR with IC50 range from 0.032 to 0.80 mg/mL. Moreover, procyanidin B2 had good affinity for HIV-1 PR and CatL PR protein, respectively. These findings suggest S. parviflora leaves can be used for treating HIV and procyanidin B2 may play a role in antiviral protease.

Dielectric spectroscopy investigation on the interaction of poly(diallyldimethylammonium chloride) with sodium decyl sulfate in aqueous solution.

The interaction between poly(diallyldimethylammonium chloride) (PDADMAC) and ionic surfactant sodium decyl sulfate (C(10)SO(4)Na) in aqueous solution was investigated by means of dielectric relaxation spectroscopy. To better understand the interaction, the dielectric behaviors of PDADMAC solution and C(10)SO(4)Na solution were also separately studied. For PDADMAC solution, two relaxations were observed, which were attributed to the polarization of loosely bound counterions along the directions parallel and perpendicular to the PDADMAC chain. For C(10)SO(4)Na solution, dielectric relaxation was observed at submicellar concentrations, which is ascribed to the counterion diffusion around premicelles. For the aqueous solutions of a PDADMAC/C(10)SO(4)Na mixture with different C(10)SO(4)Na concentrations, three surfactant concentration regions characterized by different dielectric behaviors were observed. The dielectric behavior in different regions was discussed through comparing it with that of PDADMAC solution and C(10)SO(4)Na solution. The possible interaction pattern and microstructure of the PDADMAC/C(10)SO(4)Na complex were proposed on the basis of the dielectric behavior.

Hydrogenated and fluorinated host-guest surfactants: complexes of cyclodextrins with alkanes and fluoroalkyl-grafted alkanes.

A novel type of surfactants named "host-guest surfactants" were designed and synthesized. The headgroup and hydrophobic tail of the new surfactants are connected by supramolecular interactions rather than covalent bonds. The inclusion complexes of a series of cyclodextrins (CDs) and alkanes/fluoroalkyl-grafted alkanes were synthesized and measured by surface tension, XRD, XPS, TGA, and NMR spectroscopy. The methyl-ß-CD/hexadecane complex showed surface activity relative to those conventional hydrogenated surfactants. For the inclusion complex of hydroxypropyl-α-CD/C(8)F(17)SO(2)NHC(8)H(17), the structure was locked by subtle intermolecular recognition, which ensured the surprising surface activity similar to common excellent fluorinated surfactants. This surfactant, which was fabricated from nonsurface-active even insoluble components, showed the prospect that its surface activity might also be destroyed by introducing appropriate small species to extrude the guest from the cavity.

Aggregation behavior of N-alkyl perfluorooctanesulfonamides in dimethyl sulfoxide solution.

N-alkyl perfluorooctanesulfonamides (C8F17SO2NHCnH2n+1, FC8-HCn, n = 2, 4, 6, 8) were shown to form aggregates in dimethyl sulfoxide (DMSO). Surface tension results revealed that the dissolution of FC8-HCn reduced the surface tension of DMSO in a manner analogous to common surfactants in aqueous solutions. Maximum surface excess amount (Gamma(max)) and minimum surface area per molecule (Amin) at the air-liquid interface were estimated. Gamma(max) decreases and Amin increases with an increase of the hydrocarbon chain length of FC8-HCn. Steady-state fluorescence and NMR measurements demonstrated that both fluorocarbon and hydrocarbon chains of FC8-HCn molecules were incorporated inside the aggregates. UV-vis spectroscopy confirmed the formation of aggregates and determined the critical micelle concentration (cmc) of FC8-HC6 and FC8-HC8 solutions. The thermodynamic parameters DeltaG(0)(agg), DeltaH(0)(agg), and DeltaS(0)(agg) for the aggregate formation of FC8-HCn in DMSO derived from the temperature dependence of the cmc revealed that the aggregate formation is an enthalpy-driven process, which was further confirmed by isothermal titration calorimetry (ITC) measurements. Moreover, the absolute values of DeltaG(0)(agg) and DeltaH(0)(agg) increase with an increase of the hydrocarbon chain length of FC8-HCn at 298 K.

NMR studies on binding sites and aggregation-disassociation of fluorinated surfactant sodium perfluorooctanoate on protein ubiquitin.

The fluorinated surfactant sodium perfluorooctanoate (SPFO) could bind onto ubiquitin (UBQ) and induce the unfolding of UBQ. By using (15)N-edited heteronuclear single-quantum coherence (HSQC) NMR and (19)F NMR to monitor (15)N-labeled UBQ and SPFO, respectively, the binding sites and the aggregation process of SPFO on UBQ at various SPFO concentrations were observed. A detailed process from specific binding to cooperative binding of SPFO on UBQ, and a detailed structure change of UBQ upon the increase of SPFO concentration were obtained. The refolding of UBQ in UBQ-SPFO complex was carried out by adding cationic surfactant. It was shown that added cationic surfactants formed mixed micelles with SPFO and resulted in the dissociation of the UBQ-SPFO complex, and consequently, most ubiquitin could be refolded to its native state.

Demicellization of a mixture of cationic-anionic hydrogenated/fluorinated surfactants through selective inclusion by alpha- and beta-cyclodextrin.

The interactions between alpha- and beta-cyclodextrin (alpha-/beta-CD) and an equimolar mixture of octyltriethylammonium bromide (OTEAB) and sodium perfluorooctanoate (SPFO) were studied by 1H and 19F NMR, surface tension, conductivity, and dynamic light scattering. It was shown that beta-CD could destroy the mixed micelles of OTEAB-SPFO by selective inclusion of SPFO. As beta-CD was added, the system was observed to undergo a process like this: beta-CD preferentially included SPFO to form 1:1 beta-CD/SPFO complexes. As the inclusion of SPFO was almost saturated, the mixed micelles broke and all OTEAB was released and exposed to aqueous surroundings. Then 1:1 beta-CD/OTEAB and 2:1 beta-CD/SPFO complexes significantly formed simultaneously. Contrary to beta-CD, alpha-CD exhibited selective inclusion to OTEAB and only weak association with SPFO. alpha-CD could also destroy the mixed micelles of OTEAB-SPFO; however, the demicellization ability of alpha-CD is much smaller than that of beta-CD. These conclusions were also well supported by the calculations of binding constants and DeltaG degrees . Different from the complexes of CD/conventional surfactants, the complexes of beta-CD/SPFO or alpha-CD/OTEAB formed by selective inclusion of CD in the mixed cationic-anionic surfactants may have contributed to the surface activity of the aqueous mixtures. The complexes of alpha-CD/OTEAB showed much more significant contribution to the surface activity than that of the complexes of beta-CD/SPFO.

Protein-surfactant interaction: differences between fluorinated and hydrogenated surfactants.

The interactions of proteins with fluorinated/hydrogenated surfactants were investigated by circular dichroism and turbidity measurement. Pairs of fluorinated and hydrogenated surfactants with similar critical micelle concentrations (cmc), including sodium perfluorooctanoate/sodium decylsulfate and lithium perfluorononanoate/sodium dodecylsulfate were compared in view of their interactions with proteins including BSA, lysozyme, beta-lactoglobulin and ubiquitin. It was found that fluorinated surfactants exhibited stronger interactions with proteins than hydrogenated ones, which, however, depended on the structures of both proteins and surfactant molecules. If the proteins are very stable, or the surfactant-protein interactions are very strong, such differences between the two kinds of surfactants might be indistinguishable.

NMR studies on selectivity of beta-cyclodextrin to fluorinated/hydrogenated surfactant mixtures.

The interactions between beta-cyclodextrin (beta-CD) and the equimolar/nonequimolar mixtures of sodium perfluorooctanoate (C(7)F(15)COONa, SPFO) and sodium alkyl sulfate (C(n)H(2n+1)SO(4)Na, C(n)SO(4), n = 8, 10, 12) were investigated by 1H and 19F NMR. It showed that beta-CD preferentially included the fluorinated surfactant when exposed to mixtures of hydrogenated (C(n)SO(4)) and fluorinated (SPFO) surfactants, notwithstanding whether the hydrogenated surfactant C(n)SO(4) was more or less hydrophobic than the SPFO. Such preferential inclusion of the fluorinated surfactant continued to a certain concentration of beta-CD at which time the C(n)SO(4) was then observed to be included. The longer the hydrocarbon chain of C(n)SO(4) the lower the concentration of beta-CD at which the hydrogenated surfactants began to show inclusion. The inclusion process can be qualitatively divided into three stages: first, formation of 1:1 beta-CD/SPFO complexes; second, formation of 1:1 beta-CD/C(n)SO(4) complexes; and finally, formation of 2:1 beta-CD/SPFO complexes upon further increase of beta-CD concentration. In the concentration range studied, during the last stage of inclusion both 2:1 beta-CD/C(12)SO(4) and 2:1 beta-CD/SPFO complexes appear to be simultaneously formed in the system of beta-CD/SPFO/C(12)SO(4) but not in either the systems of beta-CD/SPFO/C(8)SO(4) or beta-CD/SPFO/C(10)SO(4). The selective inclusion of the shorter fluorocarbon chain surfactant might be attributed to the greater rigidity and size of the fluorocarbon chains, compared to those of the hydrocarbon chains, which provide for a tighter fit and better interaction between the host and guest. This latter effect appears to dominate the increase in hydrophobic character as the carbon chain length increases in the hydrogenated series.

Interaction between lysozyme and mixtures of cationic-anionic surfactants decyltriethylammonium bromide-sodium decylsulfonate.

The interaction of lysozyme with the mixtures of cationic-anionic surfactants decyltriethylammonium bromide-sodium decylsulfonate (C10NE-C10SO3) was investigated by turbidity, circular dichroism (CD) and lysozyme activity assay. At pH 3.0, the mixtures of C10NE-C10SO3 formed precipitates with lysozyme at a wide range around the equal molar ratio of C10NE to C10SO3. Homogeneous solutions were formed when the mixtures of C10NE-C10SO3 were far from equimolar. CD and lysozyme activity assay showed that lysozyme was in different state in the C10SO3-rich and C10NE-rich mixtures of C10NE-C10SO3. Lysozyme structure changed in C10SO3-rich C10NE-C10SO3 mixtures, while was almost kept in native state in C10NE-rich ones.

Study of tetrabutylammonium perfluorooctanoate aqueous solutions with two cloud points by dielectric relaxation spectroscopy.

Dielectric relaxation spectra of tetrabutylammonium perfluorooctanoate (TBPFO), an anionic fluorocarbon surfactant with two cloud points in aqueous solution, were investigated in the frequency range from 40 Hz to 110 MHz. Striking dielectric relaxations were observed when both the temperature-dependent and concentration-dependent phase transitions in TBPFO aqueous solution occurred. The changes in dielectric relaxation and the distribution of dielectric parameters were consistent with the phase boundaries of the phase diagram. In the first homogeneous phase region, two relaxations of rodlike micelles appeared at about 100 kHz and 5 MHz, which originated from the diffusion of the free counterions in the directions of the long axis and the short axis of rodlike micelles, respectively. With increasing temperature, two relaxations gradually turned to one as a result of the formation of connected or entanglement points between the wormlike micelles. The lengths of the long half-axis and the short half-axis of the rodlike micelles, as well as the average distance of the connected or entanglement points of the wormlike micelles, were evaluated by the obtained relaxation times.

Interactions of beta-lactoglobulin with sodium decylsulfonate, decyltriethylammonium bromide, and their mixtures.

The interactions of beta-lactoglobulin (BLG) with anionic surfactant sodium decylsulfonate (C10SO3), cationic surfactant decyltriethylammonium bromide (C10NE), and the mixtures of cationic-anionic surfactants (C10NE-C10SO3) were investigated by circular dichroism (CD) and fluorescence methods. At pH 7.0, C10NE and the C10NE-rich surfactant mixtures of C10NE-C10SO3 could form precipitates with BLG, while C10SO3, equimolar mixtures of C10NE-C10SO3, or C10SO3-rich mixtures of C10NE-C10SO3 form homogeneous solutions with BLG. CD observed that both C10NE and C10SO3 could change the BLG structure. The effects of the mixtures of C10NE-C10SO3 on BLG structure depended on the ratio of C10NE to C10SO3. The C10NE-rich or the C10SO3-rich mixtures of C10NE-C10SO3 could significantly affect BLG structure, while the equimolar mixtures of C10NE-C10SO3 exhibited weaker interaction with BLG. Fluorescence measurements showed that both C10NE and C10SO3 could induce the enhancement of fluorescence of BLG, and C10NE enhanced the BLG fluorescence more than C10SO3 did. The effect of the mixtures of C10NE-C10SO3 on the fluorescence of BLG became stronger with the increase of the molar fraction of C10NE in C10NE-C10SO3 mixtures.

Effect of cationic surfactants on the interaction between sodium perfluorooctanoate and beta-lactoglobulin.

The interaction between the fluorocarbon surfactant, sodium perfluorooctanoate (SPFO), and beta-lactoglobulin (BLG) was studied. In particular, the effects of cationic surfactants, such as alkyltriethylammonium bromide (C(n)NE, n=8, 10, 12), on SPFO-BLG interaction were examined. It was shown that the anionic fluorocarbon surfactant, SPFO, was a strong denaturant of BLG. The ability of SPFO to denature BLG could be weakened by the addition of C(n)NE. The effect of C(n)NE on SPFO-BLG interaction was related to the hydrocarbon chain length of C(n)NE, and also the molar ratio of the added C(n)NE to the SPFO in SPFO-BLG solutions ([C(n)NE]/[SPFO]). Our findings might provide a way to design surfactant systems that are less denaturing to proteins or tailor the ability of surfactant to denature proteins through the appropriate mixing with other surfactants.

Interaction between bovine serum albumin and equimolarly mixed cationic-anionic surfactants decyltriethylammonium bromide-sodium decyl sulfonate.

The interactions of bovine serum albumin (BSA) with the anionic surfactant sodium decylsulfonate (C10SO3), the cationic surfactant decyltriethylammonium bromide (C10NE) and equimolarly mixed cationic-anionic surfactants C10NE-C10SO3 were investigated by surface tension, viscosity, dynamic light scattering (DLS) and circular dichroism (CD). It was shown that the single ionic surfactant C10SO3 or C10NE has obvious interaction with BSA. The presence of C10SO3 or C10NE modified BSA structure. However, the equimolarly mixed cationic-anionic surfactants C10NE-C10SO3 showed very weak interactions with BSA. The surface tension-log concentration (gamma-logC) plot for the aqueous solutions of C10NE-C10SO3/BSA mixtures coincided with that of C10NE-C10SO3 solutions. Viscometry showed that there is no significant change in the rheological properties for the C10NE-C10SO3/BSA mixed solutions. DLS showed that BSA monomers and mixed aggregates of C10NE-C10SO3 existed in the C10NE-C10SO3/BSA mixed solutions. From CD spectra no obvious modification of BSA structure in the presence of C10NE-C10SO3 mixtures was observed. The weak interactions between BSA and C10NE-C10SO3 might be explained in terms of the very low critical micelle concentration (cmc) of C10NE-C10SO3 mixtures that made the concentration of ionic surfactant monomers much lower than that needed for inducing the modification of BSA structure. In other words, the very strong synergism between oppositely charged cationic and anionic surfactants makes the formation of cationic-anionic surfactant mixed aggregates in the bulk solution a more favorable process than binding to proteins.

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.

Two cloud-point phenomena in tetrabutylammonium perfluorooctanoate aqueous solutions: anomalous temperature-induced phase and structure transitions.

This paper reported the phase behavior and aggregate structure of tetrabutylammonium perfluorooctanoate (TBPFO), determined by differential scanning calorimeter, electrical conductivity, static/dynamic light scattering, and rheology methods. We found that above a certain concentration the TBPFO solution showed anomalous temperature-dependent phase behavior and structure transitions. Such an ionic surfactant solution exhibits two cloud points. When the temperature was increased, the solution turned from a homogeneous-phase to a liquid-liquid two-phase system, then to another homogeneous-phase, and finally to another liquid-liquid two-phase system. In the first homogeneous-phase region, the aggregates of TBPFO were rodlike micelles and the solution was Newtonian fluid. While in the second homogeneous-phase region, the aggregates of TBPFO were large wormlike micelles, and the solution behaved as pseudoplastic fluid that also exhibited viscoelastic behavior. We thought that the first cloud point might be caused by the "bridge" effect of the tetrabutylammonium counterion between the micelles and the second one by the formation of the micellar network.

Effect of surfactant head group size on polyelectrolyte-surfactant interactions: steady-state and time-resolved fluorescence study.

Interactions between sodium poly(acrylate) (NaPAA) and dodecyltrimethyl/ethyl/propyl/butylammonium bromide (C12NM, C12NE, C12NP, and C12NB) were studied. Variation of the physicochemical properties of the surfactants and polyelectrolyte-surfactant mixtures, such as critical micelle concentration (cmc), critical aggregation concentration (cac), micellar micropolarity, aggregation number, and pyrene lifetime, were determined by steady-state and time-resolved fluorescence methods. It is shown that the surfactant head group size has a striking effect on the interaction between surfactant and polyelectrolyte. The interaction is weakened gradually when the surfactant head group is increased from trimethyl to tripropyl, which might be owing to the increase of the steric hindrance between the polyelectrolyte chain and micellar surface. But when the head group is tributyl, the interaction is enhanced and stronger than that between C12NP and NaPAA. This might be explained by the self-association of the C12NB head groups.