Effects of surface-active chemicals on microbial adhesion

Summary A simple, continuously circulating fed-batch culture system of microorganisms was designed and used to study the adhesion of mixed microbial cultures to surfaces of 316 stainless steel, Admiralty brass, and wood. The adhesion of the microbes to the surfaces was monitored by scanning electron microscope analysis. Eighteen non-toxic, non-ionic, or anionic surface-active compounds were tested for efficacy as inhibitors of microbial adhesion to stainless steel and wood surfaces. A rating system was devised to correlate efficacy with the degree of biomass adhered to 316 stainless steel, although correlation could not be made with wood. A correlation was also found between the ability of a compound to lower surface tension and its ability to prevent microbial adhesion.     

Hydrophilic carotenoids: surface properties and aggregation of an astaxanthin-lysine conjugate, a rigid, long-chain, highly unsaturated and highly water-soluble tetracationic bolaamphiphile

The surface and aggregation properties of a synthetic, highly water-soluble carotenoid, the tetracationic astaxanthin-lysine conjugate (Asly), have been examined through measurements of surface tension, optical absorption and dynamic light scattering. The following parameters were determined: critical aggregation concentration c(M), surface concentration Gamma, molecular area a(m), free energy of adsorption and aggregation (DeltaG(ad) degrees and DeltaG(M) degrees , respectively), and the aggregate size r(H). The compound forms true monomolecular solutions in water below c(M); aggregates emerge only at rather high concentrations (> or =2.18 mM).     

A hierarchy of lipid constructs for the sperm plasma membrane

We have presented a series of lipid constructs as models of the sperm plasma membrane. We also isolated the plasma membrane from rabbit sperm cells and characterized the lipid composition. The behavior of these various membrane systems was evaluated using a vesicle leakage assay, in which surfactant (nonoxynol-9, N-9; or benzalkonium chloride, BZK) exposure induced membrane permeabilization. These studies shed light on the relative importance and significance of particular components present in the lipid constructs. In particular, a highly unsaturated phospholipid component characterized by an ether-linkage to position 1 of the glycerol backbone (as opposed to the more conventional ester linkage) as well as the presence of sulfogalactosyl ceramide were found to have an effect on the surfactant-induced leakage response. The presence of cholesterol had the greatest influence on membrane behavior. The construct series also demonstrated the ability of the surfactants studied to discriminate between different membrane systems. We found that N-9 displayed little sensitivity to membrane composition while BZK showed specific behavior with the various membrane systems.     

On the effect of surface active agents and their structure on the temperature-induced changes of normal and waxy wheat starch in aqueous suspension. Part I. Pasting and calorimetric studies

Pasting and calorimetric studies of normal and waxy wheat starch were performed in the presence of a series of ionic (sulphates, trimethyl ammonium bromides) and non-ionic (monoglycerides, maltosides) short (12 carbon atoms) and long (16 carbon atoms) n-alkyl chain surfactants. With the exception of the alkyl ammonium bromides, all of the short chain surfactants lower the pasting temperature (PT) in normal wheat starch, while the long chain surfactants have the opposite effect. Contrary, regardless of their chain length, all ionic surfactants lower the PT in waxy wheat starch while the non-ionic surfactants induce small, sometimes almost negligible changes in the PT. Calorimetric studies revealed the absence of a direct connection between the effect of surfactants on the onset of the starch gelatinization transition and the PT. However, in the presence of all surfactants, except the alkyl ammonium bromides, the PT of normal wheat starch was found to lie within or very close the temperature range within which the dissociation of the amylose–surfactant complexes takes place. Waxy wheat starch, in contrast, pasted at temperatures that fell within the temperature range of the starch gelatinization transition. This is taken as evidence of the existence of a correlation between the PT and the dissociation of the amylose–surfactant complexes.     

Removal of nonionic surfactants from wastewater using a constructed wetland

Removal of nonionic surfactants from municipal wastewater using a constructed wetland with a horizontal subsurface flow was studied in 2009 and 2010. Extraction spectrophotometry with 3′,3″,5′,5″‐tetrabromophenolphthalein ethyl ester and KCl served to determine the analyte concentrations. Triton^® X‐100 was used as a standard to express the nonionic‐surfactant concentrations. Anionic and cationic surfactants were shown not to interfere during the determination. Nonionic surfactants were degraded (to products undeterminable by the method) with a high average efficiency that reached 98.1% in 2009 and 99.1% in 2010, respectively. The average concentration of nonionic surfactants at the inflow was 0.978 mg/l, while it was close to the limit of quantification at the outflow (0.014 mg/l). A significant fraction of nonionic surfactants (38.7%) was already degraded during the pretreatment, and only 14.0% of the nonionic surfactants remained in the interstitial H₂O taken in the vegetation bed at a distance of 1 m from the inflow zone at a 50‐cm depth. Nonionic surfactants were degraded both under aerobic and anaerobic conditions.     

Reactivity of trypsin in reverse micelles: neglected role of aggregate size compared to water-pool components

The catalytic efficiency of trypsin was estimated in cationic reverse micelles as a function of the concentration of water-pool components and aggregate size to determine their independent influence on enzyme activity. The variation in the aggregate size/water-pool size was achieved by changing both the W0 (mole ratio of water to surfactant) and the headgroup area of surfactant through introduction of hydroxyethyl groups at the polar head. The local molar concentrations of water present inside the water-pool ([H2O]wp) of different cationic reverse micelles across varying W0 was estimated using a modified phenyl cation-trapping protocol. The [H2O]wp in cationic reverse micelles (surfactant/isooctane/n-hexanol/water) increases with W0 and attains the molarity of normal water beyond W0=40 irrespective of the nature of headgroup. Concurrently, the catalytic activity of trypsin compartmentalized within the water-pool increases with the increase in [H2O]wp upto an optimal W0=40 in organized solutions of any surfactant. The aggregate size (determined by static light scattering) also increases expectedly with W0 and noticeably with the area of the surfactant headgroup at similar W0. Since the enzyme activity rises both with the increase in water-pool size and [H2O]wp, trypsin's efficiency was compared with these two parameters across reverse micelles of varying surfactant headgroup size at similar W0 to determine their probable independent influence in regulating the enzyme activity. Noticeably, the efficiency of trypsin rises two to ninefold in spite of the [H2O]wp being distinctly lower in case of hydroxyethyl group substituted surfactants compared to cetyltrimethylammonium bromide w/o microemulsions at similar W0. Thus, the influence of the aggregate size possibly plays an important role alongwith the [H2O]wp in modulating the enzyme activity.     

Hydrophilic carotenoids: surface properties and aggregation behavior of a highly unsaturated carotenoid lysophospholipid

The water dispersibility of a hydrophobic carotenoid has been greatly enhanced by using it as the acyl part in the synthesis of a highly unsaturated lysophospholipid. Dynamic light scattering has revealed the formation of stable aggregates with an average hydrodynamic radius of a few nanometers, and absorption spectra show that the aggregates can withstand the addition of ethanol or acetonitrile until the volume fraction of water falls below 70 and 62%, respectively. The properties of the carotenoid phospholipids have been characterized by determining surface tension, critical micelle concentration, surface concentration, molecular area, free energy of adsorption and micellation, adsorption-micellar energy relationship, and equilibrium constants.     

Oxidation of D-glucose in the presence of 2,2'-bipyridine by CrVI in aqueous micellar media: a kinetic study

The kinetics of Cr(VI) oxidation of D-glucose to the corresponding lactone in the presence and absence of 2,2'-bipyridine (bipy) has been carried out under the conditions, [D-glucose](T) > [Cr(VI)](T) at different temperatures in aqueous micellar media. The monomeric Cr(VI) species has been found to be kinetically active in the absence of bipy whereas in the bipy-catalysed path, the Cr(VI)-bipy complex has been found to be the active oxidant. In the bipy-catalysed path, the Cr(VI)-bipy complex undergoes nucleophilic attack by the substrate to form a ternary complex. The ternary complex spontaneously experiences a redox decomposition (through two-electron transfer) in the rate-determining step leading to the product lactone and Cr(IV)-bipy complex. The Cr(IV)-bipy complex then takes part in faster steps in the further oxidation of D-glucose and is ultimately converted into a Cr(III)-bipy complex. In the uncatalysed path, the Cr(VI)-substrate ester experiences acid catalysed redox decomposition (two-electron transfer) in the rate-determining step. The uncatalysed path shows a second order dependence on [H(+)] and a first order dependence on each of the reactants [D-glucose](T) and [Cr(VI)](T). In contrast, the bipy-catalysed path shows a first order dependence on each of the reactants [H(+)], [D-glucose](T) and [Cr(VI)](T). The bipy-catalysed path is first order in [bipy](T). These observations remain unaltered in the presence of externally added surfactants. The effect of the cationic surfactant, N-cetylpyridinium chloride (CPC) and anionic surfactant, sodium dodecyl sulfate (SDS) on both the uncatalysed and bipy-catalysed path has been studied. CPC inhibits both the uncatalysed and bipy-catalysed path, while SDS catalyses these reactions. The observed micellar effects have been explained by considering hydrophobic and electrostatic interactions between the surfactants and reactants.     

Direct conversion of xylan into alkyl pentosides

Xylan has been used as a raw material in the synthesis of butyl, octyl and decyl glycosides. Mixtures of d-xylose-, l-arabinose- and d-glucose-based surfactants were obtained under smooth conditions with high yields in a one-pot process. The surface activities of octyl and decyl glycosides thus obtained have been studied and compared with that of pure alkyl d-xylosides. The results have confirmed that the new synthetic approach described in this paper is a potentially economical and efficient method for the preparation of environmentally friendly surfactants.     

Enzyme-catalyzed Preparation of Novel Fatty Acid Derivatives of Pyridoxine with Surfactant Activity

A series of novel fatty acid derivatives of pyridoxine, one of the three members of the vitamin B 6 group, has been prepared. These products were obtained using an enzymatic approach. Several lipases catalyzed esterification and transesterification reactions of pyridoxine with carboxylic acid or alkyl carboxylates showed a remarkable regioselective behavior; only monoacyl derivatives were obtained. The surfactant activity, composition and clean enzymatic methodology applied in the preparation of these products make them useful as ingredients in cosmetic and pharmaceutical formulations or food additives.