1 Agua y Efecto Hidrofóbico

2 The Water Environment 70% of cell is water Hydrogen bond Hydrophilic and hydrophobic Acid and base Proton and hydroxyl Non-covalent interactions in water: Ionic bonds, hydrogen bonds, van der waals attractions, hydrophobic “effect” (force)

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7 Acid Donate a proton Base Absorb a proton or donate OH - NH3+H2O->NH4 + +OH - NaOH->Na + +OH -

8 Ionic bonds in Water

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10 Since butane and acetone are both organic compounds having a C— C and C—H backbone, they are soluble in the organic solvent CCl 4. Butane, which is nonpolar, is insoluble in H 2 O. Acetone is soluble in H 2 O because it contains only three C atoms and its O atom can hydrogen bond with an H atom of H 2 O. Physical Properties—Solubility Introduction to Organic Molecules and Functional Groups

11 To dissolve an ionic compound, the strong ion-ion interactions must be replaced by many weaker ion-dipole interactions. Physical Properties—Solubility Introduction to Organic Molecules and Functional Groups

12 The size of an organic molecule with a polar functional group determines its water solubility. A low molecular weight alcohol like ethanol is water soluble since it has a small carbon skeleton of  five C atoms), compared to the size of its polar OH group. Cholesterol has 27 carbon atoms and only one OH group. Its carbon skeleton is too large for the OH group to solubilize by hydrogen bonding, so cholesterol is insoluble in water. Physical Properties—Solubility Introduction to Organic Molecules and Functional Groups

13 The nonpolar part of a molecule that is not attracted to H 2 O is said to be hydrophobic. The polar part of a molecule that can hydrogen bond to H 2 O is said to be hydrophilic. In cholesterol, for example, the hydroxy group is hydrophilic, whereas the carbon skeleton is hydrophobic. Physical Properties—Solubility Introduction to Organic Molecules and Functional Groups

14 Vitamins are either lipid or water soluble. Introduction to Organic Molecules and Functional Groups Application—Vitamins

15 Water is an effective solvent as it can form hydrogen bonds. – Water clings to polar molecules causing them to be soluble in water.  Hydrophilic - attracted to water – Water tends to exclude nonpolar molecules.  Hydrophobic - repelled by water

16 Water transports molecules dissolved in it – Blood, a water-based solution, transports molecules of nutrients and wastes organisms – Nutrients dissolved in water get transported through plants – Unicellular organisms that live in water absorb needed dissolved substances

17 Soap: Soap molecules have two distinct parts—a hydrophilic portion composed of ions called the polar head, and a hydrophobic carbon chain of nonpolar C—C and C—H bonds, called the nonpolar tail. Application—Soap Introduction to Organic Molecules and Functional Groups

18 Introduction to Organic Molecules and Functional Groups Application—The Cell Membrane

19 Transport Across a Cell Membrane: Polar molecules and ions are transported across cell membranes encapsulated within molecules called ionophores. Ionophores are organic molecules that complex cations. They have a hydrophobic exterior that makes them soluble in the nonpolar interior of the cell membrane, and a central cavity with several oxygens whose lone pairs complex with a given ion. Introduction to Organic Molecules and Functional Groups Application—The Cell Membrane

20 Transport Across a Cell Membrane: Introduction to Organic Molecules and Functional Groups Application—The Cell Membrane

21 Several synthetic ionophores have also been prepared, including one group called crown ethers. Crown ethers are cyclic ethers containing several oxygen atoms that bind specific cations depending on the size of their cavity. Application—The Cell Membrane Introduction to Organic Molecules and Functional Groups

22 Properties of Liquids Surface tension is the amount of energy required to stretch or increase the surface of a liquid by a unit area. Strong intermolecular forces High surface tension 11.3

23 Properties of Liquids Cohesion is the intermolecular attraction between like molecules 11.3 Adhesion is an attraction between unlike molecules Adhesion Cohesion attracted to glass attracted to each other

24 Cohesion Water clings to polar molecules through hydrogen bonding – Cohesion refers to attraction to other water molecules.  responsible for surface tension  a measure of the force necessary to stretch or break the surface of a liquid

25 – Adhesion refers to attraction to other substances.  Water is adhesive to any substance with which it can form hydrogen bonds. Adhesion

26 Capillary action water evaporates from leaves = transpiration adhesion, cohesion and capillary action All thanks to hydrogen bonding! water taken up by roots

27 trees have specialized structures to transport water: xylem and phloem “plumbing” water molecules are “dragged” from the roots to the top of the tree by capillary action and cohesion: hydrogen bonds help water molecules to each other

28 Properties of Liquids Viscosity is a measure of a fluid’s resistance to flow Strong intermolecular forces High viscosity

29 Maximum Density 4 0 C Ice is less dense than water Density of Water 11.3 Water is a Unique Substance

30 La naturaleza dipolar de la molécula de agua en modelos: (a) de esferas y varillas, y (b) espaciales.  en modelos: (a) de esferas y varillas, y (b) espaciales.  hay un ordenamiento tetraédrico de las uniones O—H y de los pares de electrones libres del oxígeno.  los H tienen cargas parciales positivas y el O carga parcial negativa.  (c) dos moléculas de agua formando un puente hidrógeno.

31 Cada molécula de agua forma el máximo de 4 puentes hidrógeno en una red cristalina regular.  Cada molécula de agua forma el máximo de 4 puentes hidrógeno en una red cristalina regular.  En el agua líquida, cada molécula forma un promedio de 3.4 puentes hidrógeno con otras moléculas de agua.  La red cristalina del hielo ocupa mas espacio que el mismo número de moléculas de agua líquida. El hielo es menos denso que el agua líquida y por eso flota. Estructura del hielo

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34 Fatty Acids

35 Phospholipid (amphipathic)

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38 La unión hidrofóbica (1) Los compuestos apolares restringen la movilidad de los puentes hidrógeno del agua y producen cambios energéticos desfavorables en la estructura del agua

39 La unión hidrofóbica (2) Los ácidos grasos de cadena larga tienen cadenas alquílicas hidrofóbicas, que al ser introducidas en el agua, se rodean de moléculas de agua altamente ordenadas

40 Cuando las moléculas de ácidos grasos se agrupan lateralmente disminuye el número de moléculas de agua “ordenadas”  Cuando las moléculas de ácidos grasos se agrupan lateralmente disminuye el número de moléculas de agua “ordenadas”  Similarmente al agruparse en micelas, los acidos grasos exponen una superficie hidrofílica y minimizan el ordenamiento de las moléculas de agua. La micela se estabiliza por el efecto entrópico de aumentar el agua desordenada La unión hidrofóbica (3)

41 Vista superior de la generación de una unión hidrofóbica Cada cadena hidrocarbonada (de 9 C) está rodeada por 4 columnas de 6 moléculas de agua cada una. La asociación de dos moléculas de ácido cáprico (10 C) elimina 2 columnas de moléculas agua de la “celda del solvente”  G =  H – T  S  H = H 2 –H 1 y  S = S 2 – S 1 Cálculo de  H (para el complejo molecular descripto): Ruptura de 12 uniones H 2 O/CH 2 = kJ Formación de 9 uniones =H 2 C/H 2 C= - 36 kJ Formación de 6 uniones H 2 O/H 2 O kJ  H = - 36 kJ  H = - 36 kJ

42 Cálculo de  S: Asimilando el cambio a agua (s) => agua (l) Asimilando el cambio a agua (s) => agua (l) con  S = 22 J/K. mol de agua y 12 moles de agua con  S = 22 J/K. mol de agua y 12 moles de agua (22 J/K x 12 x 300 K) = 79.2 kJ T  S = - 79 kJ (22 J/K x 12 x 300 K) = 79.2 kJ T  S = - 79 kJ A los dominios (espacios) hidrofóbicos compartidos entre moléculas, que excluyen a las moléculas de agua, se los denomina unión hidrofóbica. En realidad, no hay una unión hidrofóbica, sino una serie de atracciones tipo van der Waals y tipo London sumados a los puentes hidrógeno del solvente (agua). Las uniones hidrofóbicas son responsables de la formación de micelas, monocapas y bicapas lipídicas, membranas biológicas y plegamientos de proteínas.  G =  H – T  S  G = - 36 kJ – 79 kJ  G = kJ Proceso espontáneo

43 Membranas Biológicas Constituidas por una bicapa de fosfolípidos y proteínas integrales y periféricas (Singer y Nicholson, 1961)

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45 La Nación, jueves 9 de octubre de 2003 Nobel de Química 2003: hallazgos sobre diminutos canales de la membrana celular