Monomolecular Surface Films Research Articles

Aquatain\xae causes anti-oviposition, egg retention and oocyte melanization and triggers female death in Aedes aegypti

BackgroundIn arboviral disease systems where the virus can be transmitted from male to female vectors and from one generation to the next, targeting the female (especially when she is gravid) can help alter the persistence of the virus in nature and its transmission. A typical example is Aedes aegypti, which has become unmanageable due to the development of insecticide resistance. Despite evidence that monomolecular surface films prevent the selection of genetic resistance, their potential in Aedes vector control remains largely unexplored.MethodsWe examined the oviposition, egg retention, oocyte melanization, and female mortality of the Cayman Islands strain of Ae. aegypti, using choice (balanced and unbalanced) and no-choice bioassays involving Aquatain® Mosquito Formulation (AMF; Aquatain Products Pty Ltd.), a polydimethylsiloxane–based liquid used for mosquito control.ResultsWhen presented with similar opportunities to oviposit in two sites treated with AMF and two other sites with untreated water (control), egg deposition rates were significantly higher in the untreated water sites than in the AMF-treated sites (P < 0.05). We also observed a matching pattern of egg deposition preference in environments with more options in terms of AMF-treated sites. Females laid significantly more eggs when water was the only available medium than when all sites were treated with AMF (P < 0.05). Also, significantly more mature eggs were withheld in the AMF no-choice environment than in the no-choice test involving only water (P < 0.05). Internal oocyte melanization was not observed in females from the oviposition arenas with the lowest AMF presence (equal-choice and water-based no-choice); in contrast, this physiological response intensified as the number of AMF-treated sites increased. Female death occurred at high rates in AMF-treated environments, and this response increased with the increasing presence of such egg deposition sites.ConclusionsThis study demonstrated that AMF acted as a deterrent signal to ovipositing Ae. aegypti and as an indirect adulticide. These results suggest that AMF may be a promising control tool against the dengue vector, and this warrants further evaluation under field settings.Graphical

Aquatain® Mosquito Formulation (AMF) for the control of immature Anopheles gambiae sensu stricto and Anopheles arabiensis: dose-responses, persistence and sub-lethal effects.

BackgroundPersistent monomolecular surface films could benefit larval source management for malaria control by reducing programme costs and managing insecticide resistance. This study evaluated the efficacy of the silicone-based surface film, Aquatain® Mosquito Formulation (AMF), for the control of the Afrotropical malaria vectors, Anopheles gambiae sensu stricto and Anopheles arabiensis in laboratory dose–response assays and standardized field tests.MethodsTests were carried out following guidelines made by the World Health Organization Pesticide Evaluation Scheme (WHOPES). Sub-lethal effects of AMF were evaluated by measuring egg-laying and hatching of eggs laid by female An. gambiae s.s. that emerged from habitats treated with a dose that resulted in 50% larval mortality in laboratory tests.ResultsBoth vector species were highly susceptible to AMF. The estimated lethal doses to cause complete larval mortality in dose–response tests in the laboratory were 1.23 (95% confidence interval (CI) 0.99-1.59) ml/m2 for An. gambiae s.s. and 1.35 (95% CI 1.09-1.75) ml/m2 for An. arabiensis. Standardized field tests showed that a single dose of AMF at 1 ml/m2 inhibited emergence by 85% (95% CI 82-88%) for six weeks. Females exposed as larvae to a sub-lethal dose of AMF were 2.2 times less likely (Odds ratio (OR) 0.45, 95% CI 0.26-0.78) to lay eggs compared to those from untreated ponds. However, exposure to sub-lethal doses neither affected the number of eggs laid by females nor the proportion hatching.ConclusionAMF provided high levels of larval control for a minimum of six weeks, with sub-lethal doses reducing the ability of female mosquitoes to lay eggs. The application of AMF provides a promising novel strategy for larval control interventions against malaria vectors in Africa. Further field studies in different eco-epidemiological settings are justified to determine the persistence of AMF film for mosquito vector control and its potential for inclusion in integrated vector management programmes.

Slicks as Indicators for Marine Processes

Monomolecular surface films (sea slicks) are well known to dampen small-scale waves at the water surface, thereby influencing transport processes at the air-sea interface. Because of their strong wave-damping capacity, they can often be observed, not just on synthetic aperture radar imagery, but also on imagery acquired in the visible and infrared spectral ranges. Because sea slicks tend to accumulate at the water surface along lines of, for example, current shear in fronts and eddies, they can be used as proxies for observing such marine processes from space. We demonstrate how well sea slicks are suited to indicate marine processes in the coastal zone. A slick's damping capability depends on the surfactant concentration on the sea surface and, thus, on the compression status of the slick-forming material. Furthermore, we show that slick signatures can be used to derive surface current vectors at higher spatial resolution than that of numerical models.

Wet Chemical Treatment in Hydrazine-Sulfide Solutions for Sulfide and Nitride Monomolecular Surface Films on GaAs(100)

GaAs surface chemical passivation by wet chemical treatments in hydrazine-sulfide solutions with different pH values has been studied by X-ray photoelectron spectroscopy and spectroscopic ellipsometry. It is found that highly alkaline (pH 12) solutions result in a coherent monomolecular film of gallium nitride, while treatment in buffered solutions yields a surface layer of gallium sulfide. Both nitride and sulfide surface films are found to be stable against oxidation in air ambient over months, attesting to the validity of the wet chemical treatment in hydrazine sulfide solutions for chemical passivation of the GaAs(100) surface. The chemical mechanism for formation of the surface nitride and sulfide films is presented and discussed.

Wind wave tank measurements of wave damping and radar cross sections in the presence of monomolecular surface films

Measurements of the damping of small gravity and gravity‐capillary water surface waves covered with monomolecular organic films of different viscoelastic properties were performed in the wind wave tank facility of the University of Hamburg. The wind speed dependence of the radar cross sections for X and Ka band was measured with upwind looking microwave antennas. It is shown that Marangoni damping theory, which describes the damping of water surface waves by viscoelastic surface films, is not the only damping mechanism in wind wave tank experiments where the wind sea is not fully developed. The other source terms of the action balance equation, i.e., the energy input into the water waves from the wind, the nonlinear wave‐wave interaction, and the dissipation by wave breaking, are affected differently by the various substances. It is hypothesized that this difference is caused by the different viscoelastic properties of the substances, i.e., by the different intermolecular interactions of the film molecules. A slight dip in the wind dependence of the radar cross section at Ka band at wind speeds of 8–9 m/s was measured, which corresponds to comparable reductions of the mean squared wave height and wave slope. Polarization ratios (i.e., the ratios of the radar backscatter at vertical and horizontal polarization) higher than those predicted by simple Bragg scattering theory for X band at low wind speeds and different incidence angles are explained within a (three‐scale) composite‐surface model. At higher wind speeds, where the polarization ratio decreases rapidly, breaking by wedges and spilling breakers is hypothesized to become more dominant. The dependence of the polarization ratio on the coverage of the water surface with a slick is explained qualitatively by means of the composite‐surface model. Finally, it is stated that wind wave tank measurements in the presence of monomolecular surface films are useful for the verification of theories concerning radar backscattering, wave damping, and wind‐wave and wave‐wave interactions.

Surface strain modulation of insoluble surface film properties

The complex dispersion relation of capillary waves on water has been measured in a wavelength regime (λ∼1–2 cm) of interest to radar imaging. Two noninvasive sensors: a capacitive wave height antenna and a one-dimensional scanning laser slope gauge, are used to study the alteration of surface tension and surface elastic modulus in the presence of monomolecular surface films. On a static water surface, these sensors are compared to accepted standard techniques. The surface tension results are compared to a Wilhelmy plate while the elastic modulus results are compared to equations of state obtained by Langmuir trough techniques. The sensors are then employed to measure the response of surface film properties to surface areal strains for film pressures and strain rates, which are comparable to natural films in the presence of ship-generated surface currents. In the experiments reported in this paper, only insoluble surfactants are used. The monolayer surface films considered in this study are found to exhibit higher elastic modulus (∼8 mN/m) at small surface pressure (π≤1 mN/m) than expected from previous work reported in the literature. The response of these films to surface strain is consistent with our static surface measurements. The modulation of film parameters is found to be in phase with internal wave-generated oscillatory surface strain with periods on the order of 9 s. This implies that the film conforms to the strained water surface with negligible slippage in this regime. These measurements demonstrate the capability of this approach to continuously monitor surface films in situ with detector system response time of the order of 1 s. The technique is suited to large or deep containers and is applicable to sheltered ocean environments.

Thermal anomalies of the surface potential induced by monomolecular surface films

Surface potential measurements performed in the presence of 1-hexadecanol and Z-9-octadecen-1-ol monolayers within a temperature range between 283 and 303 K revealed a thermal anomaly at 288 and 303 K. The addition of NaCl increased the anomalous effect induced by a 1-hexadecanol surface film, while in the presence of a Z-9-octadecen-1-ol monolayer the magnitude of the thermal anomaly of a salt-free subphase and a 0.25 M NaCl solution was comparable.

The primary structure and some kinetic properties of phospholipase A2 from sheep pancreas

AbstractThe complete amino acid sequence of ovine phospholipase A2 (EC 3.1.1.4) has been determined. The enzyme consists of a single polypeptide chain containing 123 amino acids, crosslinked by seven disulfide bridges, with a molecular weight of 13804. The enzyme differs at six positions from phospholipase A2 isolated from bovine pancreas1. Both enzymes show similar affinities for Ca2+ ions and hydrolyze monomeric substrates with comparable efficiency.Using monomolecular surface films as a substrate, the ovine enzyme was shown to be able to hydrolyze lipids at slightly higher surface pressures than the bovine enzyme. Direct‐binding studies showed the higher affinity of the ovine enzyme for micelles of the substrate analogue, n‐hexadecylphosphocholine.We suggest that this increased affinity is attributed to a substitution of Asn122 of the bovine enzyme for a tyrosine residue in its ovine counterpart.

Attenuation of wind waves by monomolecular sea slicks and the Marangoni Effect

Previous observations of wind wave damping by monomolecular surface films (“slicks”) have shown a pronounced energy detraction (“dip”) in the short gravity wave range of the wind wave spectra. In this work, wind wave tunnel experiments with mechanically generated water waves have supplied experimental evidence which clearly shows that this dip is predominantly caused by the film‐induced “Marangoni effect.”

Wave damping by monomolecular surface films and their chemical structure. Part II: Variation of the hydrophilic part of the film molecules including natural substances

Wave damping by monomolecular surface films and their chemical structure. Part II: Variation of the hydrophilic part of the film molecules including natural substances

The thermal anomaly of relaxation effects in monomolecular surface films

A thermal anomaly of relaxation effects within an 9-octadecen-l-ol Z-isomer (“oleyl alcohol”) surface film has been found at 303 K by measuring the time dependence of surface pressure decrease at constant compression areas A 1 = 0.08 nm 2/molecule and A 2 = 0.25 nm 2/molecule in an automatically working Langmuir-trough. The application of different spreading solvents (ethanol, heptane) produced qualitatively different results, however, in both cases the thermal anomaly of the relaxation effect could be established.

The effect of monomolecular surface films on the microwave brightness temperature of the sea surface

It is pointed out that monomolecular surface films of biological origin are often encountered on the ocean surface, especially in coastal regions. The thicknesses of the monomolecular films are of the order of 3 x 10 to the -9th m. Huehnerfuss et al. (1978, 1981) have shown that monomolecular surface films damp surface waves quite strongly in the centimeter to decimeter wavelength regime. Other effects caused by films are related to the reduction of the gas exchange at the air-sea interface and the decrease of the wind stress. The present investigation is concerned with experiments which reveal an unexpectedly large response of the microwave brightness temperature to a monomolecular oleyl alcohol slick at 1.43 GHz. Brightness temperature is a function of the complex dielectric constant of thy upper layer of the ocean. During six overflights over an ocean area covered with an artificial monomolecular alcohol film, a large decrease of the brightness temperature at the L-band was measured, while at the S-band almost no decrease was observed.

Attenuation of wind waves by artificial surface films of different chemical structure

Experiments in a wind wave tunnel have shown that spectra of wind generated waves are modified by monomolecular surface films. Apart from the well known decrease of energy density two additional effects have been observed: a shift of the energy peak maximum and a dip in the short wavelength region of the gravity wave spectrum. Two mechanisms which would cause the shift of the peak maximum and one mechanism possibly contributing to the spectrum dip in the short gravity wave range are discussed.

Regulation of phospholipase A2 activity by different lipid-water interfaces.

The activity of pancreatic phospholipase A2 (EC 3.1.1.4) is controlled not only by the architecture of the catalytic site, but is also strongly dependent on the penetrating power of the interface recognition site and the packing density of the lipid-water interface. The influence of the latter two factors on the interface activity has been investigated using chemically modified phospholipases A2 in which the NH2-terminal L-Ala8 has been replaced by DL-[3-13C]Ala, or in which the polypeptide chain has been elongated with DL-[3-13C]Ala. The [DL-(3-13C)Ala8]phospholipase A2 could be resolved into the pure diastereoisomers, [D-(3-13C)Ala8]phospholipase A2 and [L-(3-13C)Ala8]phospholipase A2 by elution on Sephadex G-100 in the presence of a micellar lipid-water interface, as well as by conventional ion exchange chromatography on carboxymethylcellulose. Similar procedures did not effect, however, a separation of DL-[3-13C]Ala7-phospholipase A2 into their respective diasteroisomers, indicating the strategic role of the NH2-terminal L-Ala8 residue in the interaction process between the enzyme and lipid-water interfaces. Kinetic experiments using various micellar short chain lecithins revealed the apparent absence of an interface recognition site in [D-(3-13C)Ala8]- and DL-[3-13C]Ala7-phospholipase A2, while these proteins still possess considerable enzymatic activity toward monomeric substrates. In contrast, however, kinetic experiments using monomolecular surface films, allowing a continuous change in surface density of the substrate molecules, revealed that [D-(3-13C)Ala8]- and DL-[3-13C]Ala7-phospholipase A2 at low surface pressure possess about 60 and 30% of the interface activity of native phospholipase A2, respectively. These results therefore suggest that the modified phospholipases A2 do possess an interface recognition site although less powerful as compared to that of the native enzyme, enabling the estimation of the surface density of micellar short chain lecithins.

Surface activity of extracts of the lungs and other organs

Monomolecular surface films on the border-line of the "liquid-air" phases were observed to be formed in the water-saline extracts of the lungs and of the other organs. The surface films were compressed and extended on Wilhelmy's balance; the isotherm surface tension (ST)-square typical of the solutions of the surface-active materials (SAM) were recorded. Analogous curves with the minimum ST below 12 din/cm were recorded in testing the SAM monolayers placed on the liquid lining of the volatile solvent. Pulmonary surfactants differed from the SAM of other organs by the highest capacity to lower the ST in compression of the monolayer.

Comments on “Retardation of Water Drop Evaporation with Monomolecular Surface Films”

Comments on “Retardation of Water Drop Evaporation with Monomolecular Surface Films”

Comments on “Retardation of Water Drop Evaporation with Monomolecular Surface Films”

Comments on “Retardation of Water Drop Evaporation with Monomolecular Surface Films”

Lipid structures

AbstractMuch of the function of lipids, as in shortenings, confections, biological membranes, etc., depends on the structures they exhibit, i.e., their crystalline and mesomorphic states. Triglycerides may serve as a point of departure for considering the crystal state of lipids. The three principle cross‐sectional arrangements of long chains‐α, β′ and β‐in which there is kinship to hydrocarbons, offer a major basis for classification. Different crystal forms are rheologically different. Complications in the chain length direction lead to stepped configurations in the methyl planes and to double and triple chain length structures. A detailed consideration of the time‐honored melting point alternation of homologs sheds light on the lipid crystal picture. A startling feature is the catalysis of isomerization by the solid state of diglycerides, with a consequent shift in equilibrium far toward 100% 1,3‐diglyceride. Stepwise reversible transformations, as in hydrocarbons, are documented for high molecular weight 1‐monoglycerides. A common feature, the sharp drop with mixture of stable form melting points, to “expose” metastable forms as stable forms for intermediate compositions is strikingly exhibited by fatty alcohols. The two bases for mesomorphism, or liquid crystal formation, among lipids are discussed: (1) dichotomy between molecular moieties in degree of polarity, as in phospholipids; and (2) dichotomy in molecular geometry as in cholesteryl esters. The former type is associated with three main basic arrangements‐smectic or lamellar, middle or hexagonal (normal and reversed), and viscous isotropic or cubic (normal and reversed). The latter is associated with two main arrangements‐cholesteric (essentially limited to cholesteryl compounds) and smectic. The importance of mesomorphism in consideration of membranes and emulsions is emphasized. Developments in understanding the structures of interfacial lipid states (including monomolecular surface films) and the correspondence of interfacial with bulk states is a matter of great continuing interest.

Retardation of Water Drop Evaporation with Monomolecular Surface Films

The influence of a variety of water-insoluble monomolecular films on the evaporation rate of 50 to 500 μ diameter water drops was determined at 25C and 50% relative humidity. The results indicate that only linear polar molecules capable of close packing can form monomolecular films which inhibit the gas transport of water molecules across an air–water interface. Slight deviations from straight-chain linearity due to substituents on the hydrocarbon backbone of the surface-active molecule prevent molecular adlineation, alter the physical state of the monolayer, and sharply reduce its ability to retard evaporation. The influence of impurities which do not affect evaporation was evaluated by studying mixed films which contained both linear and nonlinear molecules. For each of the chemical systems studied, the rate of evaporation decreased to a constant value as the surface film was compacted on the shrinking drop surface. Evaporation rates were decreased up to 17-fold by the most effective fatty alcohol and ester monolayers. Literature claims of much greater retardation effectiveness are attributed to evaporation measurements of the film-forming organic material rather than that of the water drop. The implications of these chemical effects to fog and haze stabilization and to the possible modification of atmospheric processes are discussed.

Factors affecting the use of monomolecular surface films to control oil pollution on water

Factors affecting the use of monomolecular surface films to control oil pollution on water