Lec1 Chemical Nature of Water PDF

# Biomedical Importance of Water * Predominant chemical component of living organisms * Able to solvate wide range of organic and inorganic molecules due to it's dipolar structure * Exceptional capacity for hydrogen bond formation * An Excellent Nucleophile * Regulation of water balance * Propensit...

# Biomedical Importance of Water * Predominant chemical component of living organisms * Able to solvate wide range of organic and inorganic molecules due to it's dipolar structure * Exceptional capacity for hydrogen bond formation * An Excellent Nucleophile * Regulation of water balance * Propensity to dissociate into hydroxide ions and protons ## Water * A water molecule ($H_2O$) is made up of three atoms: one oxygen and two hydrogen. ## Water - An Ideal Solvent * Water molecule has an irregular, slightly skewed tetrahedron structure with oxygen at its center. * The strongly electronegative oxygen attracts electrons away from hydrogen nuclei leaving them with a partial charge, while the two unshared electron pairs constitute a region of local negative charge. ## Water is a Polar Molecule * A molecule with electrical charge distributed asymmetrically about it's structure is referred to as Dipole. * Water's strong dipole is responsible for it's high dielectric constant. * Enables water to dissolve large quantities of charged compounds such as salts. * Water has a dipole moment * "like dissolves like" * Oxygen is more electronegative than hydrogen so there is an uneven distribution of charge in this H-O bond. * Uneven distribution is called a dipole and the bond is said to be polar. ## Water is Polar * In each water molecule, the oxygen atom attracts more than it's "fair share" of electrons * The oxygen end "acts" negative * The hydrogen end "acts" positive * Causes the water to be POLAR * However, water is neutral (equal number of $e^-$ and $p^+$)-- zero net charge. ## Hydrogen Bonds - Water Molecules * Formed between a highly electronegative atom of a polar molecule and a hydrogen. * One hydrogen bond is weak but many hydrogen bonds are strong. ## Hydrogen Bonds * Extraordinary properties that are a result of hydrogen bonds: * Cohesive behavior. * Resists changes in temperature. * High heat of vaporization. * Expands when it freezes. * Versatile solvent. * Hold water molecules together. * Each water molecule can form a maximum of 4 hydrogen bonds. * The hydrogen bonds joining water molecules are weak, about 1/20th as strong as covalent bonds. * They form, break, and reform with great frequency. ## Hydrogen Bonding of Water * One $H_2O$ molecule can associate with 4 other $H_2O$ molecules. * Ice: 4 H-bonds per water molecule. * Water: 2.3 H-bonds per water molecule. ## Interaction Between Water Molecules * Negative oxygen end of one water molecule is attracted to the positive hydrogen end of another water molecule to form a hydrogen bond. ## Water is an Excellent Nucleophile * Water, whose two lone pairs of sp3 electrons bear a partial negative charge, is an excellent nucleophile. * Nucleophilic attack by water generally results in the cleavage of the amide, glycoside, or ester bonds that hold biopolymers together. This process is termed hydrolysis. ## Nucleophilic Nature of Water * Chemicals that are electron-rich (nucleophiles) seek electron-deficient chemicals (electrophiles). * Nucleophiles are negatively charged or have unshared pairs of electrons --> attack electrophiles during substitution or addition reactions. * Examples of nucleophiles: oxygen, nitrogen, sulfur, carbon, water (weak). ## Properties of Water: * Polar molecule * Cohesion and adhesion * High specific heat * Density - greatest at 4°C * Universal solvent of life ## Universal Solvent * Because of water's polarity, many compounds dissolve in water. * Why is this important? * Most biochemical reactions involve solutes dissolved in water ## Polarity of Water * This polarity allows it to dissociate ions in salts and bond to other polar substances such as alcohols and acids, thus dissolving them. Its hydrogen bonding causes its many unique properties, such as having a solid form less dense than its liquid form, a relatively high boiling point of 100°C for its molar mass, and a high heat capacity. * Because of the electron arrangements in the water molecule, a polarity results that allows water to form hydrogen bonds with one another and other polar substances. * Polar substances are hydrophilic (water-loving). * Nonpolar ones are hydrophobic (water-dreading) and are repelled by water. ## Properties of Water * Cohesion * Adhesion * High Specific Heat * High Heat of Vaporization * Less dense as a solid ## Cohesion * Attraction between particles of the same substance (why water is attracted to itself) * Results in surface tension (a measure of the strength of water's surface). * Produces a surface film on water that allows insects to walk on the surface of water. ## Surface Tension * Helps insects walk across water. ## Adhesion * Attraction between two different substances. * Water will make hydrogen bonds with other surfaces. * Capillary action - water molecules will "tow" each other along when in a thin glass tube. * Example: transpiration process which plants and trees remove water from the soil, and paper towels soak up water ## #3. Adhesion * $H_2O$ sticks to other material. ## Adhesion Causes Capillary Action * Which gives water the ability to "climb" structures. ## (continues...) * #4 Capillary Action: Helps $H_2O$ rise against gravity from roots to leaves in plants. * #5 Density: ice is less dense than water causing it to float. ## Water is Less Dense as a Solid * Ice is less dense as a solid than as a liquid (ice floats). * Liquid water has hydrogen bonds that are constantly being broken and reformed. * Frozen water forms a crystal-like lattice whereby molecules are set at fixed distances. ## Why is Density Important? * The floating ice slows the freezing process by insulating the water underneath, which contributes to the moderate temperatures on earth. * The layer of ice prevents many lakes from freezing solid, allowing fish and other organisms to survive under the ice. ## Why Does Ice Float on Water? * In liquid state, water molecules are closely held together by weak hydrogen bonds. * On reaching solid state, hydrogen bonds become stable arranging the water molecules far apart from each other. * This causes ice to have a lesser density than water, making it float. ## Water is Less Dense as a Solid: * Which is ice and which is water? ## High Specific Heat * Amount of heat needed to raise or lower 1g of a substance by 1°C. * Water resists temperature change both for heating and cooling. * Water can absorb or release large amounts of heat energy with little change in actual temperature. ## #7 High Specific Heat * It means that water takes longer to heat up and to cool down. * Water in a pond will stay relatively the same from day to night. * Bodies of water near cites take longer to heat up and longer to cool down than do land masses. * These cities will tend to have less extreme temperatures than inland cities. ## High Heat of Vaporization * Amount of energy to convert 1g of a substance from a liquid to a gas. * In order for water to evaporate, hydrogen bonds must be broken. ## High Heat of Vaporization * Water's heat of vaporization is 540cal/g. ## #6 Universal Solvent * Water is considered an universal solvent because it can dissolve many substances. * Ions and hydrophilic solutes dissolve easily in water. * The solvent properties of water are greatest with respect to polar. * Figure 2: Salt dissolved in water. * Water, the solvent, forms spheres of hydration around the ions of salt. Salt is the solute because it is dissolved by the water. * Salt is composed of Na and Cl atoms in an ionic bond. * Salt in a solution of water will look like this when dissolved. ## Types of Mixtures * **Solutions:** * Solute: substance that is being dissolved (salt). * Solvent: dissolves the solute (ex. water). * **Suspensions:** * Substances that separate into tiny pieces but don't dissolve. ## Physical Properties of Water * Freezing and boiling points: Water freezes at 0 degrees Celsius and boils at 100 degrees Celsius under normal atmospheric pressure. * Density: It reaches its maximum density at 4 degrees Celsius. * High Specific Heat: It requires a significant amount of energy to change its temperature, aiding in climate regulation. * Ability to Dissolve Substances: It is an excellent solvent, useful for transporting nutrients. * Surface Tension: It possesses a strong surface layer, forming droplets. * Capillarity: It can move against gravity in small spaces. * Common Liquid State: On Earth, it is primarily found in a liquid state. ## Chemical Properties of Water * **Polarity:** Water is a dipole, with a positive charge on hydrogen and a negative charge on oxygen. * **Ability to Dissolve Substances:** Acts as a solvent due to its polarity, dissolving a wide range of substances. * **Acid-Base Reaction:** Can act as an acid (releasing protons) or as a base (accepting protons). * **Autoionization:** Self-ionizes into hydronium ions (H3O+) and hydroxide ions (OH). * **High Dielectric Constant:** Facilitates ionic dissociation and the formation of aqueous solutions. * **Buffer Capacity:** Can resist changes in pH. * **Chemical Reactivity:** Participates in various chemical reactions, such as hydrolysis. ## Hydrophilic & Hydrophobic * **Hydrophilic** - water loving - compounds can dissolve in it. * **Hydrophobic** - non-polar molecules that cannot dissolve in water -- waxes, oil. * Non-polar solvents like chloroform or benzene -- poor solvents for polar molecules. ## Did You Know?? * Life began in water. * About ¾ of Earth is covered in water. * All living things need water. Your cells are approximately 70-95% water. * Water is the "universal solvent" because it can dissolve many things! ## What Does Water do for You? * **Forms saliva (digestion)** * **Keeps mucousal membranes moist** * **Allows body's cells to grow, reproduce and survive** * **Needed by the brain to manufacture hormones and neurotransmitters.** * **Regulates body temperature (sweating and respiration)** * **Acts as a shock absorber for brain and spinal cord** * **Flushes body waste, mainly in urine** * **Lubricates joints** * **Water is the major component of most body parts** * **Converts food to components needed for survival - digestion** * **Helps deliver oxygen all over the body** ## Functions of Water in Human Body * Transports nutrients and oxygen into cells * Regulates body temperature * Detoxifies * Moisturizes the air in lungs * Helps with metabolism * Protects vital organs * Helps organs to absorb nutrients * Protects and moisturizes our joints ## Problems Related to Water * Hypovolemia * Hypervolemia ## Dehydration & Rehydration * A diagram of a brain with text "Dehydration," an arrow pointing to a thought bubble with text "Thirst," and an arrow pointing to a thought bubble with text "Sense of Thirst," leading to a stomach with text "Ingestion of water," leading to a thought bubble with text "Short-term Inhibition of thirst" and a thought bubble with text "Long-term Inhibition of thirst," connecting to a thought bubble with text "Distends stomach and intestines." An arrow points to a thought bubble with text "Cools and moistens mouth," connecting to a woman with text "Rehydration," and an arrow pointing to a thought bubble with text "Rehydrates blood." Two arrows point to a thought bubble with text "Increased Blood Osmolarity" and the other pointing to a thought bubble with text "Reduced Blood Pressure." The arrow pointing to "Reduced Blood Pressure" leads to a thought bubble with text "Renin". These two thought bubbles lead to a thought bubble with text "Reduced Salivation" and a thought bubble with text "Dry Mouth. The thought bubble with text "Reduced Blood Pressure" leads to a thought bubble with text "Angiotensin II. The thought bubble with text "Angiotensin II" leads to a thought bubble with text "Stimulates Hypothalamic Osmoreceptors" and the thought bubble with text "Increased Blood Osmolarity" leads to a thought bubble with text "Stimulates Hypothalamic Osmoreceptors." ## References - Images of Books: * The Absolute, Ultimate Guide to Lehninger _Principles of Biochemistry_ Study Guide and Solutions Manual, Seventh Edition, Marcy Osgood, Karen Ocorr. * Harper's Illustrated Biochemistry, 32nd edition, Victor W. Rodwell, David A. Kennelly, P. Anthony Weil.