Organic Chemicals in the Environment Where are they found? What are the effects do they have? Surface effects Membranes Waxes Foams Soil - Humus The air-water interface The surface tension of water is 0.073 N/m. Ions can increase this value somewhat to 0.075 N/m. However, organic compounds Tend to lower the value. The surface tension of organic liquids (e.g. octane, benzene etc.) range from 0.020 to 0.050 N/m. There are two types of surface adlayers on water. 1. Organic thin films such as oil spills (prior to oxidative weathering). These compounds are both insoluble and less dense than water. 2. Surfactants are amphipathic molecules. There are dry surfactants such as detergents (mostly hydrophobic) and wet surfactants such as proteins (mostly hydrophilic). Surface tension Liquids tend to adopt shapes that minimize their surface area. This places the maximum number of molecules in the bulk. Droplets of liquids tend to be spherical because a sphere is the shape with the smallest surface-to-volume ratio. The work needed to change the area by dσ is: dw = γdσ The coefficient γ is called the surface tension. It has dimensions of energy per unit area (J/m 2 ). At constant volume and temperature the work of surface formation is equal to the Helmholtz free energy: dA = γdσ Since dA < 0 is a spontaneous change surfaces tend to contract. Lipids and Surfactants Both lipids and surfactants consist of a hydrophobic tail region and a hydrophilic head group (amphipathic). Both lipids and surfactants will orient with their head groups pointed towards the water interface and their tails sequestered from water. Lipids have the ability to form a bilayer. This property makes these molecules the constituents of biological membranes. Bilayers can be gel-like or crystalline. They can have a planar phase or form hexagonal phase. Surfactants can tend to form micelles. Micelles are spherical. The hydrophobic tails form the interior and the charged head groups are on the surface. Biochemistry of Lipids, Lipoproteins and Membranes, Vance & Vance, Elsevier 1996 Lipid polymorphism Lipid structure Representative lipids are shown in Figure to the right. There are two acyl chains on a glycerol. The third site is a phosphodiester with a number of possible groups indicated. The fluid mosaic model of membranes Biochemistry of Lipids, Lipoproteins and Membranes, Vance & Vance, Elsevier 1996 Plasma membrane Cytosol Membrane asymmetry The inner and outer leaflets of membrane bilayers have different compositions. Erythrocytes are the most studied. The cytosolic side is composed of PE and PS. The PE distribution is ca. 80% in the inner membrane and 20% in the outer membrane. PS is negatively charged and PE is moderately negative in charge. The inner membrane is thus largely negative. The outer membrane consists of PC, sphingomyelin, and glycolipids. Cholesterol is also important and associates with the membrane to provide added fluidity. Plasma membranes have equimolar quantities of cholesterol. By contrast, the endoplasmic reticulum and mitchondrial membranes have small amounts of cholesterol. Detergents and Lysophospholipids Detergents are amphipathic molecules that can have charged or uncharged head groups and single hydrophobic tails. If one of the acyl chains is cleaved from a lipid then a lysophospholipid is created. Other associating molecules include aromatic or fused ring compounds (dyes, purines, pyrimidines) and alicyclic fused ring compounds (bile salts, cholesterol etc.). SDS O O O OH R Lysophospholipid S O - O O O Transmembrane Potential Membranes are essential for life. They provide a compartment for chemistry to occur separate from the environment. Living organisms have also evolved to use membranes for generation and storage of energy using photosynthesis. This is done by pumping protons across a membrane to generate a transmembrane potential. The transmembrane electrical potential is represented as the voltage difference of the inside with respect to outside. We express the potential as V (unit is the volt). In chemistry, the Nernst equation is used to describe the dependence of the oxidation potential on concentration. The symbol is E (or E o ) and the unit is also the volt. [...]... carbon-chains and one terminal hydroxyl (ω-position) and other hydroxyl groups in secondary positions The cutin polymer has been found to be based on the inter-esterification of hydroxyacids (head-to-tail in a linear form or cross-linked) and of glycerol esterified with various hydroxy-fatty acids Graca J et al., Phytochemistry 2002, 61, 205 Cutin structure The cuticle is part of the epidermis Cutin is the. .. low intake of essential minerals, especially young children and those in developing countries, this effect can be undesirable A common way in developing countries to increase the bioavailability of minerals from grains and beans is using fermentation Many bacteria possess phytase activity and by fermenting grains or beans by lactic acid bacteria the phytate is destroyed and the bioavailability of the. .. process can be slow; the equilibrium expression describes concentrations when the system reaches equilibrium, not how fast it gets there Hydrogen bonding in water Hydrophobic interactions The hydrophobic effect The free energy change for transfer of hydrocarbons from organic solvent to water is positive The dominant contribution to the hydrophobic effect is the entropy In the organic phase: µH(H)... Mar Ecol Prog Ser 1996, 134, 295 Cutin is a wax found on leaves Monoacylglycerols are important in the constitution of cutin polymer Cutin is the structural component of the plant cuticle, the outermost layer of leaves and other aerial organs Waxes embedded in the cutin make the cuticle an efficient barrier against desiccation, gas exchange and pathogen attack Cutin polyester is typically composed of... water loss When moving plants from sun to shade the amount of cutin required changes due to the amount of water generated by photosynthesis The formation of a polymeric layer of molecules to for cutin is shown on the right The cutin polymer is a crosslinked set of esters of long α,ω-alcohol carboxylic acids or dicarboxylic acids Monomer composition in cutin Biochemistry of wax synthesis Acetyl co-A... B et al., Phytochemistry, 1996, 42, 501 Soil carbohydrates Soil contains organic matter only near the surface The organic compounds arise mostly from the action of microorganisms Most of the organic matter is trapped in colloids and is not in equilibrium Soil contains a number of carbohydrates and sugars comprising about 10% of the organic matter Most of it is polymeric although some monomeric sugars... •Beta-mercaptoethylamine •Pantothenic acid •Phosphate •3', 5'-adenosine diphosphate Suberin is found in bark Waxes are also found in suberin, which is a lipidic polyester present in tree barks, tuber skins and abscisic tissue of falling leaves It is also formed in plant after wounding Upon depolymerization, cork suberin releases a mixture of monomers and oligomers, including monoacylglycerols of monoacid (C22), of ω-hydroxyacids... beans Phosphorus in this form is generally not bioavailable to humans because humans lack the digestive enzyme, phytase, required to separate phosphorus from the phytate molecule Phytic acid binds to important minerals such as calcium, magnesium, iron and zinc and can therefore contribute to mineral deficiencies, as the minerals are not released from the phytate and are thus unavailable to the body Good... the electromotive force is: emf = E(+) - E(-) The free energy is G = -nFE Therefore, the standard free energy change for a redox process is ∆Go = -nF(Eoox - Eored) = -nF∆Eo Application of the Nernst equation to membrane potential The free energy per mole of solute moved across the membrane ∆Gconc = -RTln(Co/Ci) where Co is the concentration outside the membrane and Ci is the concentration inside the. .. important molecule in metabolism Its main use is to convey the carbon atoms within the acetyl group to the Krebs Cycle to be oxidized for energy production In chemical structure, acetyl-CoA is the thioester between coenzyme A (a thiol) and acetic acid (an acyl group carrier) It is also a carrier of two carbon units in fatty acid synthesis 1 Acetyl group 2 Coenzyme A •Beta-mercaptoethylamine •Pantothenic acid . Organic Chemicals in the Environment Where are they found? What are the effects do they have? Surface effects Membranes Waxes Foams Soil - Humus The. Erythrocytes are the most studied. The cytosolic side is composed of PE and PS. The PE distribution is ca. 80% in the inner membrane and 20% in the outer membrane.