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Surface and interfacial chemistry (Biosurfactants)

Our work at Surface an interfacial laboratory has emphasized on biologically active amphiphilic molecules occurring naturally (Biosurfactants) and the alike molecules produced bio- mimetically.

The term surfactant is a shortening of the words surface active agent.

Surfactants offer extraordinary benefits to many industries. They are involved in infinite number of different industrial processes and physicochemical phenomenon: Increasing mobility, increasing solubility, lubrication, removing soil (scouring), wetting, rewetting, softening, retarding dyeing rate, fixing dyes, making emulsions, stabilizing dispersions, coagulating suspended solids, making foams, preventing foam formation, defoaming, etc.

In addition they have a large number of bioactivities: Stimulate bacterial growth, toxic effects, immune stimulant, tumour growth inhibition, antibiotic, cell lysis (haemolysis), plant pathogenicity, effects on migration of human neutrophils, respiratory action (anti- asthma activity), food digestion, inhibition of cell wall synthesis, fungicidal properties or enzyme stimulation, bio regulatory effects, etc. Hence they play part in many processes in nature.

These molecules have an unlimited number of uses that involves every industry and every aspect of life: oil industry, pharmaceuticals, testing quality of condoms, hygiene an cosmetics, cement, beer and beverages, textiles, paint, detergents and cleaning, food processing, etc. the applications depend on applied properties and the mechanism of action.

A surface active molecule tends to accumulate at surface or interface causing change in the surface or interfacial tension. This leads to many different phenomenon or action such as: Emulsification, increasing wetting properties, foaming, surface medification, surface lubrication, etc., and hence the application of these molecules.

Measuring surface tension:
1. Classical methods: Contact angel, balance based methods (ring and plate methods).
2. Dynamic methods (bubble method) and droplet methods.
3. Online methods: Droplet volume method (capacitive drop tensiometer (CDT), is based on the drop volume principle in combination with a capacitive transducer),
4. In Situ force –balance tensiometer, water filled porous cup – pressure transducer. Or,
5. Tensiography (Fiber optic illuminated drop) and ( ultrasonic tensiography: ultrasonic interferometry on liquid drops)

Environmental aspects of surface tension
The surface tension in the environment changes constantly due to either surfactant pollution (household or industry ) or production of naturally occurring surfactants.

In aquatic or marine environment
The surface tension is the macroscopic demonstration of the molecular phenomena at the interface between two liquid phases. Surfactants may change a liquid's wetting characteristics causing the alteration of surface tension and consequently the mass transferring at the liquid interface. This process is of immense significance to the studying the mass transfer (of pollutants) in aquatic and marine environments.

In soils
The direction of water flow in soil is determined by the water pressures in the soil and this in turn determines the transport of chemicals in the vadose zone. These processes are also dependent on surface tension and its alterations caused by either surfactant pollution (household or industry) or by production of naturally occurring surfactants.

Surface tension in nature
Naturally occurring biosurfactants will cause a constant change in surface tension in the environment and hence destabilize the surveillance parameters : Mobility , solubility, mass transfer, bioremediation time, degradation rates, quantity -location relations.

Biosurfactants
These surfactants are produced naturally by different organisms/ microorganisms: Bacteria, algae, fungi , plants, animal cells, degradation of organic matter from organisms (fat, protein, carbohydrates, etc)

Biomimetic surfactants
Are Biosurfactant like molecules produced by chemical or enzymatic synthesis under controlled lab conditions, the aim of this type of synthesis is the production biosurfactants molecules with specific properties.

Chemical identity of Biosurfactants: sugar based, peptide based, polymers , fatty acids, etc.

Environmental uses of tensiometery
1. In situ prediction of the direction of water flow and chemical transport in the vadose zone. For this purpose the soil water pressures is measured over a prolonged space and time.
2. pollutants are measured quantitatively using pendant drop illuminated method from within by an optic fiber generator and receiver. The procedure provides intricate fingerprint tracing that generate profiles depending on the surface tension, refractive index, color and other parameters. The system is used to develop an ultra-sensitive gas detection method in which the adsorption of the target gas to the drop is detected via changes in the drop.
3. Prediction or estimation of changes of environmental parameters: Mobility , solubility, mass transfer, etc.
4. Surveillance of mass transfer in aquatic environment using in situ force-balance tensiometry, droplet volume method that allows measurements of the dynamic surface tension.
5. Controlling water quality using tensiometry (droplet volume method ) and tensiography methods (pendant drop illumination method).
6. Environmental Risk analysis and environmental impact assessment (EIA)

Projects

Naturally occurring surfactants:
- Rhamnolipids from pseudomonas sp., production and physicochemical properties.
- Sepiculisporic acid of Penicillium spiculisporum, physicochemical properties.
- Surfactin of Bacillus subtilis, physicochemical properties.

Biomimetic surfactants:
- Amino acid based surfactants, production and physicochemical properties
- Sugar based surfactants production and physicochemical properties.

Study of bioactivity:
Effects on bacteria and blood cells, etc.

Contact person: Mohamad Osman