Inclusion Of Surfactant Research Articles

Adeno-associated virus adsorption on different surfaces relevant to production of pre-clinical & clinical material

Since the concept of gene therapy was introduced in the late 1970s, recombinant Adeno-associated virus (AAV) vector has emerged as a leading drug platform for delivering treatment to patients. During the AAV production process, capsids get exposed to and interact with various surfaces including bioreactors, resins, tubing, and storage containers. These interactions potentially impact vector concentration due to surface adsorption. When evaluating drug product in both in vitro and in vivo studies, the concentration of the purified AAV vectors should be consistent. Maintaining vector concentration accuracy is critical for successful evaluation of pre-clinical and clinical-stage studies. Therefore, it is of interest to investigate the effect of contact layer adsorption on AAV concentration over time. To understand the potential effects of material surface on concentrations for two widely used serotypes, AAV8 and AAV9, this study evaluated the extent of product loss on ten commonly used contact materials: polypropylene, polystyrene, flint glass, borosilicate glass, crystal zenith, high-density polyethylene, polyethylene terephthalate glycol, polypropylene copolymer, polycarbonate, and silicon. In addition, the study examined the effect of a non-ionic copolymer surfactant, commonly used in process or in storage formulations, on adsorption. Samples and buffer controls for the two serotypes were stored in different materials in the presence and absence of the surfactant. Sample optical density (OD) measurements were used to calculate the changes in the total and in the percentage of empty capsids over time. Noticeable differences in adsorption were observed for the different serotypes and different contact layers over time when normalized to the contact area. Additionally, serotype and contact surface interactions had an impact on the percentage of empty capsids in the solution, and polypropylene showed the largest influence. Inclusion of surfactant had a variable effect depending on the surface and serotype.

Formulation and evaluation of selexipag and ezetimibe bi-layer tablet by novel approach

Hypertension and hypercholesterolemia are two common diseases that often coexist. The combined presence of hypertension and hypercholesterolemia increases considerably the risk for cardiovascular complications. Selexipag is used to treat symptoms of pulmonary arterial hypertension and Ezetimibe is a lipid-lowering compound that inhibits intestinal cholesterol and phytosterols absorption. The bilayer tablets of antilipidemic and antihypertensive can be employed for the treatment of hypertension and hypercholesterolemia together through oral administration of single tablet. The rationale for this fixed-dose combination is to co-administer two drugs acting by different mechanisms of action together, reduce dosing frequency, and increase patient compliance. In the present investigation we combine Selexipag and Ezetimibe. Immediate release layer of Selexipag was formulated using various superdisintegrants like Crospovidone, Croscarmellose sodium, and sodium starch glycolate, Microcrystalline Cellulose, Magnesium Stearate and Extended release layer of Ezetimibe was formulated using polymers and gums like Hydroxy Propyl methyl cellulose, Poly vinyl Pyrrolidone, Talc, Gaur gum, and Xanthan gum, Magnesium stearate. The disintegration and dissolution study of both layers showed that inclusion of surfactant to the tablet formulation (Immediate Release) and dissolution medium (Extended Release) enhanced the release of drugs from both layers.

Catalyzed-Mea conversion of Agro-biomass to paper-pulp: Influence of pulping additives and synergy effect on pulp screened yield

In this research work, the effect of three (3) pulping additives such as polysulfide, Anthraquinone and surfactant used in the monoethanolamine (MEA) pulping of agro-biomass, their possible interactions and synergy effect on pulp screened yield were investigated. The pulping conditions of the digester were adjusted so that the experimental design considered the following factors and levels: 75% MEA charge, 150oC cooking temperature, 90minutes cooking time, 4 to 1Liquor- Biomass ratio. Factor 1: 0, 0.25 and 0.5% Surfactant charge, Factor 2: 0, 2.0 and 4.0% polysulfide charge, Factor 3: 0, 0.25 and 0.5% anthraquinone charge. The Agro-biomass was evaluated in terms of pulp screened yield. Heating time ranged from 5 to 45minutes and maximum cooking time did not exceed 90minutes, liquor biomass ratio was 4 to 1 and Liquor charge was 75% MEA. The yield for MEA with 4% Polysulfide (PS) dosage without the inclusion of Surfactant and Anthraquinone was highest (59.08%) in all the twenty seven (27) experimental runs, but furnished the highest reject (12.26%) and an unimpressive screened yield of 46.82% standing amongst the least possible outcomes. The yield for MEA with 0.25% Anthraquinone (AQ) dosage without the inclusion of Surfactant and Polysulfide furnished a total yield of 50.32%, pulp screened yield of 50.03% with a minimal reject of 0.29 showing to be more efficient than the use of polysulfide. Monoethanolamine (MEA) pulping with 0.5% surfactant (Surf.) dosage without the inclusion of other additives i.e. AQ and PS achieved 51.12% total screened yield with a reject of only 0.33% furnishing the highest pulp screened yield (50.79%) thereby showing more efficiency amongst the three (3) pulping additives investigated in this research study base on single use. However, the result obtained from the combination of the three (3) pulping additives furnished the highest screened yield (52.43) with 4.23% reject in scenario E, experiment No. 15, involving the combination of 0.25% surfactant, 0.25% anthraquinone and 4% polysulfide charge showing the best synergistic effect. Although the highest screened yield (53.04% and the least reject (0.13%) indicating the best possible outcome amongst the entire twenty seven (27) experimental runs came from the combination of 0.25% surfactant and 2% polysulfide charge. If we have to consider the use of surfactant and polysulfide alone, the best possible outcome came from the combination of 0.25% surfactant and 2% polysulfide charge in experiment 20 of scenario G. Analyses of the overall experimental results show that there is considerable advantage and a positive synergy effect in the use of additives in pulping operation.

Effects of surfactant on morphology, chemical properties and catalytic activity of hydroxyapatite

Hydroxyapatite (HAP) was synthesised in the presence of surfactants and tested as a catalyst in CO oxidation. XRD confirmed that the characteristic HAP crystal phase was practically unaffected by the addition of surfactant. The surfactant altered both the Ca/P ratio and particle size of HAP. Catalyst tests showed that the activity of HAP increased for preparations using TWEEN, PEG and PVA. The temperature for 50% conversion, T50, values decreased from 340 °C for unmodified HAP, to 320 °C for TWEEN and to 315 °C for both PEG and PVA. This enhanced activity is rationalised by the higher BET surface areas and acid site densities in the surfactant-modified preparations: these increased from 52 m2 g−1 for HAP to 69, 76 and 68 m2 g−1, and from 101 μmol g−1 for HAP to 110, 170 and 126 μmol g−1 for TWEEN, PEG and PVA, respectively. These findings demonstrate that HAP i.e. without the addition of precious metals to either the surface or framework, is an active CO catalyst and that the straightforward inclusion of surfactant during preparation can optimise the catalytic performance.

Fabrication and Performance of Supercapacitor Devices Using Binder-Free CNT Electrodes

Electric double layer capacitors (EDLCs) are a category of supercapacitors that generally compliment the performance of batteries through delivery of high power with significantly longer cycle life. The conventional active electrode material utilized in these EDLCs is activated carbon (AC) possessing high surface area through templated porosity. However, one of the primary limitations with AC-based supercapacitors using organic electrolytes is the operational voltage maximum around 2.75 V. Operation at higher voltages that push the 2.75 V barrier is the next essential developmental breakthrough to enable significant boosts to both energy and power densities of supercapacitors. Research into alternative active electrode materials is equally critical to enable and support high voltage operation of supercapacitors. This work demonstrates the fabrication of carbon nanotube (CNT) electrodes from organic-based dispersions without the inclusion of surfactant or binder, and subsequent assembly into supercapacitor devices. The performance of pouch cells assembled from the CNT electrodes and using conventional organic electrolytes at operating voltages ≥ 2.7 V is discussed. A significant and linear voltage dependence of capacitance (~ 3 times higher than AC) was observed for cells with CNT electrodes up to operational voltages ~ 3.5 V, which are currently not achievable using AC-based cells. Repeatable charge-discharge operation of the CNT-based EDLCs was demonstrated at 3.5 V and 70°C, with consequential increase to capacitance by ~ 25 - 30 % compared to 2.7 V operation. Power and energy densities were increased by 1.5 and 2 times respectively at 3.5 V compared to operation at 2.7 V. The performance characteristics from such CNT-based pouch cells were benchmarked against commercial-grade AC supercapacitor devices using organic electrolytes and rated at 2.75 V (single cell). Long-term performance advantages were observed for the CNT-based monocells at 3.5 V and 70°C, which passed 100k cycling tests at full discharge. Under the same test conditions, commercial AC-based cells failed early during the 100k cycling. Response times approaching 2 ms (at -45° phase angle) were also demonstrated with EDLC devices using thin CNT electrodes with 1 mF capacitance. Such EDLC devices may potentially rival aluminum electrolytic capacitors (AECs) for alternating current line-filtering applications, offering significant space savings compared to the bulky AEC components. Finally, the scalable fabrication of binder-free CNT electrodes from surfactant-free dispersion of the material was demonstrated by roll-to-roll, slot-die coating onto an Al foil current collector. The processing of these conformal CNT coatings, assembly into 18650 cylindrical cells, and the resulting EDLC performance characteristics are discussed. The CNT-based 18650 cells had an average capacitance of 7 F at 2.7 V, with low average ESR of 7 mΩ at 1 kHz, and average response time of 120 ms at -45° phase angle. Figure 1

Controlling the binding of hydrophobic drugs with supramolecular assemblies of β-cyclodextrin

Supramolecular assemblies generated from self-assembling β-cyclodextrin were evaluated as hydrophobic drug carriers in vitro in aqueous conditions. The native β-cyclodextrin macrocycle was used to develop the novel host-guest assemblies with antitumor drug 2,2′-bibenzimidazole and its new derivate with n-nonyl groups at the nitrogen atoms. The morphology and sizes of these assemblies were characterized by NMR spectroscopy, DLS and TEM techniques. The interaction of the two bibenzimidazole guests with the carrier and their releasing properties under action of exogenous surfactant were investigated by means of UV–vis and fluorescence spectroscopy, DLS and TEM. The study of effect of a cationic surfactant, cetyltrimethylammonium bromide, on the stability of β-cyclodextrin–guest assemblies revealed the higher affinity of β-cyclodextrin for guest with n-nonyl groups and the higher stability of the resulting assemblies compared to those in the case of non-alkylated guest. The non-alkylated guest-rich carrier was disrupted rapidly when mixed with a surfactant trigger. The disruption of β-cyclodextrin–guest assemblies was accompanied by competitive inclusion of surfactant in β-cyclodextrin cavity which resulted in drug release from β-cyclodextrin carrier. The results of this study demonstrate the feasibility and usefulness of a trigger-responsive delivery of hydrophobic drugs using soft β-cyclodextrin assemblies.

Phenomenology and control of buckling dynamics in multicomponent colloidal droplets

Self-assembly of nano sized particles during natural drying causes agglomeration and shell formation at the surface of micron sized droplets. The shell undergoes sol-gel transition leading to buckling at the weakest point on the surface and produces different types of structures. Manipulation of the buckling rate with inclusion of surfactant (sodium dodecyl sulphate, SDS) and salt (anilinium hydrochloride, AHC) to the nano-sized particle dispersion (nanosilica) is reported here in an acoustically levitated single droplet. Buckling in levitated droplets is a cumulative, complicated function of acoustic streaming, chemistry, agglomeration rate, porosity, radius of curvature, and elastic energy of shell. We put forward our hypothesis on how buckling occurs and can be suppressed during natural drying of the droplets. Global precipitation of aggregates due to slow drying of surfactant-added droplets (no added salts) enhances the rigidity of the shell formed and hence reduces the buckling probability of the shell. On the contrary, adsorption of SDS aggregates on salt ions facilitates the buckling phenomenon with an addition of minute concentration of the aniline salt to the dispersion. Variation in the concentration of the added particles (SDS/AHC) also leads to starkly different morphologies and transient behaviour of buckling (buckling modes like paraboloid, ellipsoid, and buckling rates). Tuning of the buckling rate causes a transition in the final morphology from ring and bowl shapes to cocoon type of structure.

Formulation and in vitro evaluation of bilayer tablets of nebivolol hydrochloride and nateglinide for the treatment of diabetes and hypertension.

Diabetes mellitus (DM) and hypertension are two common diseases that often coexist. The most common cause of death in the diabetic patient is heart disease. In the present investigation we combine Nebivolol and Nateglinide for better patient compliance. IR layer was formulated using various superdisintegrants like Crospovidone, Croscarmellose sodium, and sodium starch glycolate and SR layer was formulated using polymers and gums like HPMC E15, ethyl cellulose, Gaur gum, and Xanthan gum. The disintegration and dissolution study of both layers showed that inclusion of surfactant (sodium lauryl sulphate) to the tablet formulation (IR) and dissolution medium (SR) enhanced the release of drugs from both layers. Kinetic studies of optimized IR layer (NBL8) and SR layer (N9) showed good linearity with regression coefficient of 0.9714 (Higuchi model) and 0.9931 (zero order kinetics), respectively. The above results reveal that the optimized IR layer of Nebivolol (NBL8) and SR layer of Nateglinide (N9) might be suitable for the treatment of diabetes and hypertension by sequential release of the two drugs in a bilayer tablet. IR-immediate release, SR-sustain release, NBL8-Nebivolol 8, N9-Nateglinide 9.

Control of Protein Particle Formation During Ultrafiltration/Diafiltration Through Interfacial Protection

This study investigates the mechanism of protein particle formation during ultrafiltration/diafiltration (UF/DF), finding that agitation drives particle formation by promoting protein-interface adsorption and desorption. Low conductivity and the presence of surfactant reduced the level of particle formation in small-scale stirring studies, and the same trends were observed in pumping and UF/DF. Polysorbate 80 (PS80) and hydroxypropyl-β-cyclodextrin (HPβCD) reduced particle formation in UF/DF by factors of 15 and 4, respectively. Measurements of conformational stability, colloidal stability, and surface tension demonstrated that PS80 protects against particle formation by preventing protein-interface adsorption, low conductivity improves the colloidal stability of the protein, and the mechanism of action of HPβCD remains unclear. This work demonstrates that interfacial adsorption–desorption of the protein during UF/DF is the principal cause of particle formation, that the level of surfactant-free particle formation depends on the colloidal stability of the protein, and that the inclusion of surfactant greatly reduces in-process particle formation during UF/DF.

Electrodeposition of tin-rich Cu–Sn alloys from a methanesulfonic acid electrolyte

A systematic approach for the selection of electrochemical parameters for the electrodeposition of tin-rich copper–tin alloys has been performed. This was enabled by using a Cu:Sn ratio of 1:10 in the electrolyte. The effect of this metal ion ratio in the electrolyte and surfactants on the tin content in the deposit was examined using a rotating disk electrode. Cyclic voltammetry showed that inclusion of surfactant in the electrolyte had no effect on the reduction potential of tin which remained at −0.45V. However, the reduction potential for copper decreased from −0.13 to −0.18V, thereby making alloy deposition more facile. Chronoamperometry and anodic stripping voltammetry showed that current efficiency for copper–tin deposition ranged from 92 to 95%. Electrodeposition experiments to obtain high Sn content were carried out at constant current using vitreous carbon electrodes. Deposits containing up to 96wt% tin were obtained. Cu–Sn alloys consisted of two phases, tetragonal tin and a hexagonal Cu6Sn5 intermetallic compound.

Stability of whole inactivated influenza virus vaccine during coating onto metal microneedles

Immunization using a microneedle patch coated with vaccine offers the promise of simplified vaccination logistics and increased vaccine immunogenicity. This study examined the stability of influenza vaccine during the microneedle coating process, with a focus on the role of coating formulation excipients. Thick, uniform coatings were obtained using coating formulations containing a viscosity enhancer and surfactant, but these formulations retained little functional vaccine hemagglutinin (HA) activity after coating. Vaccine coating in a trehalose-only formulation retained about 40–50% of vaccine activity, which is a significant improvement. The partial viral activity loss observed in the trehalose-only formulation was hypothesized to come from osmotic pressure-induced vaccine destabilization. We found that inclusion of a viscosity enhancer, carboxymethyl cellulose, overcame this effect and retained full vaccine activity on both washed and plasma-cleaned titanium surfaces. The addition of polymeric surfactant, Lutrol® micro 68, to the trehalose formulation generated phase transformations of the vaccine coating, such as crystallization and phase separation, which was correlated to additional vaccine activity loss, especially when coating on hydrophilic, plasma-cleaned titanium. Again, the addition of a viscosity enhancer suppressed the surfactant-induced phase transformations during drying, which was confirmed by in vivo assessment of antibody response and survival rate after immunization in mice. We conclude that trehalose and a viscosity enhancer are beneficial coating excipients, but the inclusion of surfactant is detrimental to vaccine stability.

IVH – The rise (and fall) of the surfactant dose?

The incidence (or not) of intraventricular haemorrhage (IVH) in infants receiving surfactant remains controversial. Moreover, it is well known that the incidence of IVH, adjusted for known risk factors, varies across neonatal intensive care units (NICUs) in any country. Given that a trend towards an increase in overall IVH incidence with natural surfactant was noted in the meta-analysis by Soll, an important question arises: Could a recent trend in higher concentrations/doses of natural surfactant lead to an increase in IVH? It is not suggested that there is a consistent association between surfactant treatment and IVH, but this is an interesting consideration. As surfactant treatment has consistently been shown to lower mortality, it is extremely important to ensure that this is not at the expense of increased survival of infants brain damaged by haemorrhage or ischaemia. Infants who present with respiratory distress syndrome (RDS) are extremely vulnerable, and are precisely the infants most at risk of cerebral lesions. This relevant question is applicable in South Africa and internationally, with the proposal for the inclusion of surfactant in the WHO model list of essential medicines. Since surfactant has been adopted into routine neonatal practice in South Africa, the other very important question of economic impact has shifted to questions regarding the specific preparations, number of doses, modes of administration, concomitant use of new technologies such as nasal continuous pulmonary airway pressure (nCPAP), etc. However, before stakeholders plunge headlong into an economic – or any other – argument, perhaps there is a need for greater collaboration between clinicians (and the pharmaceutical industry) in the reporting of recent trends, including adverse events in this very vulnerable group.

Micellar behavior of aqueous solutions of dodecyldimethylethylammonium bromide, dodecyltrimethylammonium chloride and tetradecyltrimethylammonium chloride in the presence of α-, β-, HP β- and γ-cyclodextrins

Conductivity, static fluorescence and 1H NMR measurements have been carried out to study the micellar behavior of aqueous solutions of dodecyldimethylethylammonium bromide (DDAB), dodecyltrimethylammonium chloride (DTAC) and tetradecyltrimethylammonium chloride (TDAC) in absence and presence of α-cyclodextrin ( α-CD), β-cyclodextrin ( β-CD), hydroxypropyl- β-cyclodextrin (HP β-CD) and γ-cyclodextrin ( γ-CD). The conductivity measurements were carried out at 298.15 K. The influence of cyclodextrins on the micellar parameters, such as cmc ∗ (apparent critical micellar concentration), β (degree of ionization) have been analyzed. Thermodynamics of the systems was discussed in terms of the change in standard free energy of micellization, Δ G m 0 . Micellization was found to be less spontaneous in presence of cyclodextrins. The fluorescence intensity of the surfactant solutions is enhanced by the addition of cyclodextrins. The association constants obtained from conductivity and fluorescence data suggest the binding of γ-CD with the surfactants to be strongest among all the cyclodextrins used. 1H NMR chemical shift changes provide powerful means for probing the cyclodextrin–micellar interactions and inclusion of surfactant is shown by the change in the chemical shift of some of the guest and host protons in comparison with the chemical shifts of the same protons in the free compounds.

Effects of interacting variables on the release properties of chloroquine and aminophylline suppositories

Purpose: The individual and interaction effects of formulation variables on the release of suppositories were investigated using a 23 factorial experimental design. The variables studied were nature of base (B), type of drug (D), and presence of surfactant (S). Method: Suppositories were formulated with theobroma oil and Witepsol H15 as bases at ‘low' and ‘high' levels respectively. Chloroquine and aminophylline, both water-soluble drugs, were incorporated as active constituents at ‘low' and ‘high' levels respectively while Tween 80 was incorporated as surfactant in some of the formulations. Disintegration time and time taken for 50% of the drug to dissolve were used as assessment parameters. Results: The inclusion of surfactant in the suppository formulation proved to be the most significant variable in the formulation. The ranking for the individual coefficient values for the formulations was S>>B>D for disintegration time DT and S>>>D>B for the dissolution parameter t50. While the ranking for the interaction effects was B-D>B-S>S-D on DT and on t50 S-D>B-S>B-D. Conclusion: The results suggest that in formulating water-soluble drugs such as chloroquine and aminophylline as suppositories in a hydrophobic base, the presence of a surfactant is the most influential variable. Keywords: Suppositories, chloroquine, aminophylline, surfactant, interacting variables. > Tropical Journal of Pharmaceutical Research Vol. 3 (1) 2004: pp. 285-290

Surfactant-induced fingering phenomena in thin film flow down an inclined plane

We consider the dynamics of a thin liquid film covered with insoluble surfactant flowing down an inclined plane. A coupled pair of nonlinear partial differential equations for the film height and surfactant concentration are derived using lubrication theory. Two configurations of fluid and surfactant are considered: constant flux and constant volume. Examination of the base states reveals the presence of propagating wave fronts in both configurations. Application of a transient growth analysis demonstrates the existence of an instability near the leading edge of the fluid that is found to be vulnerable to transverse disturbances of intermediate wavenumber. Our results illustrate that several features of the much studied uncontaminated film flow problem are modified due to the inclusion of surfactant.

Flow of surfactant-laden thin films down an inclined plane

A theory is formulated to describe the dynamics of a thin film flowing down an inclined plane laden with insoluble surfactant, present in dilute concentrations. Use of lubrication theory yields a coupled pair of partial differential equations for the film height and surfactant monolayer concentration. The contact line singularity is relieved by assuming the presence of a thin precursor layer ahead of the advancing film. Base flow solutions for a flow of constant flux are examined over various inclination angle, precursor-layer thickness, Peclet number, and capillary parameter ranges. Application of a transient growth analysis highlights the presence of an instability and the vulnerability of the flow to transverse disturbances of intermediate wavenumber. Our results reveal that several key features of the much-studied uncontaminated film flow, including stability, are modified qualitatively by the inclusion of surfactant.

Enhanced loading of water-soluble actives into bicontinuous cubic phase liquid crystals using cationic surfactants

Over the past few years, bicontinuous cubic phase liquid crystals have been investigated for their applicability to controlled delivery of active ingredients. These liquid crystals have a unique structure of interpenetrating channels of water and lipid that provides compatibility with water-soluble, lipid-soluble, and amphiphilic active ingredients. Actives tend to be stable in the matrix and the structure provides control over their release. However, loading of water-soluble actives is difficult. It is especially problematic for cubic phase liquid crystal dispersions (cubosomes) given the large fraction of bulk water present. The inherent problem reflects the preference of the water-soluble actives to associate with water rather than with the liquid crystals. Ideally, the properties of the liquid crystal can be tailored to enhance the association of the liquid crystal with the active, thereby increasing loading. It is found that the inclusion of surfactant into the liquid crystal can provide this function. This work illustrates the enhanced loading of negatively charged, water-soluble active ketoprofen by the inclusion of positively charged surfactants into the liquid crystal. Loading differences resulting from the inclusion of dioctadecyl dimethyl ammonium chloride (DODMAC) and dioctadecyl ammonium chloride (DOAC) into the liquid crystal demonstrate that the magnitude of the enhancement is dependent on the surfactant concentration and the steric nature of its head group. The upper limit of the enhancement is explored by the inclusion of di(canola ethyl ester) dimethyl ammonium chloride (DEEDAC) formulated to greater than 20 wt% and demonstrates an order-of-magnitude enhancement over previous reports. This work provides a practical demonstration of functionalizing cubic phase liquid crystals and lays the framework for future work.

Effects of Cyclodextrins as Additives on Surfactant CMC

In this paper, the effects of α, β‐cyclodextrins (β‐CD) on the critical micelle concentration (CMC) of CTAB, SDS, and Brij35 were investigated at 25°C using electrical conductivity and visible spectrophotometry. The results indicate that α, β‐CD increase the CMC of the surfactants by the competitive inclusion of surfactant in cyclodextrin. From the experimental data, an empirical formula for CMC* (apparent critical micelle concentration) of these three surfactants was obtained.

Mesoscopic Simulation of Cell Membrane Damage, Morphology Change and Rupture by Nonionic Surfactants

A new simulation method, dissipative particle dynamics, is applied to model biological membranes. In this method, several atoms are united into a single simulation particle. The solubility and compressibility of the various liquid components are reproduced by the simulation model. When applied to a bilayer of phosphatidylethanolamine, the membrane structure obtained matches quantitatively with full atomistic simulations and with experiments reported in the literature. The method is applied to investigate the cause of cell death when bacteria are exposed to nonionic surfactants. Mixed bilayers of lipid and nonionic surfactant were studied, and the diffusion of water through the bilayer was monitored. Small transient holes are seen to appear at 40% mole-fraction C 9E 8, which become permanent holes between 60 and 70% surfactant. When C 12E 6 is applied, permanent holes only arise at 90% mole-fraction surfactant. Some simulations have been carried out to determine the rupture properties of mixed bilayers of phosphatidylethanolamine and C 12E 6. These simulations indicate that the area of a pure lipid bilayer can be increased by a factor 2. The inclusion of surfactant considerably reduces both the extensibility and the maximum stress that the bilayer can withstand. This may explain why dividing cells are more at risk than static cells.

Further studies onDatura metel Linn powder I: effect of surfactants on the granule and compact properties

A study has been made of the effect of the presence of surfactant in binder mucilage on the granules and compacts of D. metel powder (DMP). The mean size, friability, sinking times and flow property of the granules have been measured. Bigger and less friable granules were produced with the presence of surfactants due to increased wettability of the hydrophobic D. metel powder (DMP). The flow rate increased while the angle of repose decreased with the presence of surfactants and increase in surfactant concentration. Inclusion of surfactant resulted in the production of weaker compacts with a reduction in disintegration times. The improved wetting of the powder resulted in the decrease in disintegration times. © 1998 John Wiley & Sons, Ltd.