Water and buffers

1. TUMS Water and buffers Azin Nowrouzi (PhD) anowrouzi@tums.ac.ir

2. WATER Microscopic Structure of waster Water molecule Ionization of Water, • Weak Acids • Weak Base • pH Buffering against pH Changes Biological buffers Water as a reactant Water as a solvent

3. Importance of water • The most abundant substance in living systems. • Makes up 70% or more of the weight of most organisms. • Living organisms depend on water for their existence. • Physical & chemical properties of water make it fit to support life: • High boiling point  water remains liquid in most seasons. • Ice less dense than water  floats on liquid water and water freezes from top to bottom. So a good insulator: a frozen layer of ice serves as a blanket that protects creatures below. • Ubiquitous solvent in cells. • Excellent solvent of polar and ionic substances. • Medium where most cell’s metabolic reactions take place. • Ionization of water and its acid-base reactions important for the functions of proteins and nucleic acids. • The Shapes of proteins and nucleic acids and structure of biological membranes are consequence of their interaction with water.

5. Hybrid orbitals - sp3 hybridization and tetrahedral bonding • Water has a simple structure. • Oxygen has 6 electrons in the outer shell: 1s2, 2s2, 2p4. • Sp3 hybridization  H—O—H bond angle is 104.5.

6. A hydrogen bond between two water molecules

7. The structure of ice

8. The structure of water is irregular

9. “Water molecule” is polar • The net charge of water molecule is zero. But O—H bond is polar because O is more electronegative than H. Sharing of electrons between H and O is unequal. • The charge on O = -0.82 and on H = +0.41. This charge separation produces permanent dipoles.

10. A water molecule

11. Hydrogen bonds - weak bonds important in the chemistry of life • Created by attraction between slightly positive regions and slightly negative regions • Hydrogen bonding occurs in many biologically important compounds • Water • DNA • Proteins

12. H-bond formation • H-bond can form when a H atom that is bonded to O or N lies within 0.27-0.30 nm of another O or N atom that has unshared e-.

13. Water molecules form H bond • Attraction between positive H and negative O of another H2O produces dipole-dipole attraction called a hydrogen bond (H bond). • H bond is 10% covalent and 90% electrostatic. • The strength of H-bond is 4 kcal/mol, less than 5% as strong as a typical covalent bond. The strength of O—H bond is 110 kcal/mol. H-bond is a weak interaction. • Notice that the hydrogen bond (shown by the dashed line) is somewhat longer(117 pm) than the covalent O—H bond (99 pm). This means that it is considerably weaker.

14. Hydrogen bond LE 2-10

15. Structure of water in ice • At any given time, most of the molecules in water are engaged in hydrogen bonding, but the lifetime of each hydrogen bond is just 1-20 picoseconds (1ps = 10-12s). • In liquid water, molecules are disorganized and in continuous motion, so that each molecule forms H-bonds with an average of only 3.4 other molecules. • In ice crystal each H2O is hydrogen bonded to 4 other H2O molecules.

16. LE 2-13 • Hydrogen bond • Ice • Liquid water • Hydrogen bonds • constantly break and re-form • Hydrogen bonds are stable

17. Microscopic structure of water • Short-lived groups of water molecules interlinked by hydrogen bonds in liquid water are called flickering clusters.

18. Flickering clusters • At any given time, most of the molecules in liquid water are engaged in hydrogen bonding, but the lifetime of each hydrogen bond is just 1 to 20 picoseconds (1 ps = 10-12 s). • Upon breakage of one hydrogen bond, another hydrogen bond forms, with the same partner or a new one, within 0.1 ps. • The apt phrase “flickering clusters” has been applied to the short-lived groups of water molecules interlinked by hydrogen bonds in liquid water. • The sum of all the hydrogen bonds between H2O molecules confers great internal cohesion on liquid water.

19. Structured Water Is Changing Models (H2O)8 Bennett Daviss The Scientist 2004, 18(21):14. (H2O)14 (H2O)17 (H2O)21 (H2O)196 (H2O)280 (H2O)more (H2O)280

20. Structured water Suggested by Prof. Martin Chaplin of the London South Bank University 2(H2O)4 (H2O)8 More dense water  Less dense water

21. محقق ژاپني با انتشار يافته‌هاي تحقيقات خود مدعي شد كه مولكول‌هاي آب نسبت به مفاهيم انساني تأثيرپذيرند.نظريه اين محقق ژاپني كه تاكنون از سوي مؤسسات علمي فيزيكي و زيست‌شناسي مورد تأييد قرار گرفته است، مبتني بر بررسي نمونه‌هاي فراواني از كريستال‌هاي منجمدشده آب و مقايسه آن با يكديگر است. http://www1.lsbu.ac.uk/water/ http://www1.lsbu.ac.uk/water/index2.html http://www.chem1.com/acad/sci/aboutwater.html • دكتر ماسارو ايموتو • Masaru imoto

22. http://www.lsbu.ac.uk/water/index2.html

23. كريستال‌هاي آب منجمدشده The messages from water

24. سلام Goldberg Variations“ آهنگ باخ رقص سنتي ژاپني(كاواچي )

25. water can have highly organized local structures when it interacts with molecules capable of imposing these structures on the water. therapeutic powers of homeopathic remedies Memory of water Organized water molecules William Royer Jr. U. of Mass. Medical school India, 2003

26. “bound water” molecules what do they do? Stabilization a b B-DNA with a spine of water molecules • Water binding in hemoglobin The crystal structure of hemoglobin, shown (a) with bound water molecules (red spheres) and (b) without the water molecules

27. ‘Bound water’ in biological systems • Intracellular water very close to any membrane or organelle (sometimes called vicinal water) • Organized very differently from bulk water • This structured water plays a significant role in governing the shape (and thus biological activity) of large folded biopolymers.

28. Water chain in cytochrome f

29. Proton and hydroxide mobility is large compared to other ions • H3O+ : 362.4 x 10-5 cm2•V-1•s-1 • Na+: 51.9 x 10-5 • Hydronium ion migration; hops by switching partners at 1012 per second.

30. Proton hopping

31. Water molecules form H-bonds with polar solutes Some biologically important H-bonds

32. Forms Hydrogen bonds with Functional Groups

33. LE 2-14 • Salt • crystal • Ion in • solution

34. Electrostatic interaction with charged solutes • When NaCl is mixed with water, a shell of water surrounds each Na+ and Cl- ion.

35. Ions change structure of liquid water • Ionic substances are soluble because the net attraction of the + and – ions for water is greater than the attraction of oppositely charged ions for each other. • Formation of the Hydration shell.

36. Structured water 2(H2O)4 (H2O)8 More dense water  Less dense water

37. STRUCTURED WATER

38. Types of ions • Structure-breaking ion 'chaotrope' (disorder-maker) (Na+) • structure-forming ion 'kosmotrope' (order-maker) (K+) • Kosmotropes shift the local equilibrium to the right. • Chaotropes shift it to the left. more dense (condensed) water  less dense water

39. Nonpolar gases are poorly soluble in water

40. Hydrocarbons in water • Hydrocarbons and nonpolar molecules are insoluble because water-water interactions are stronger than water-hydrocarbon interactions. So water molecules force nonpolar molecules together and surround them. • This phenomenon is called hydrophobic effect or hydrophobic interaction.

42. Water as a solvent Water is a polar solvent: • Compounds that dissolve easily in water are hydrophilic (Greek, “water-loving). • Nonpolar molecules that are not dissolved in water can be dissolved in nonpolar solvents (chloroform, and benzene). These nonpolar molecules are called hydrophobic (water-fearing). • Compounds that contain regions that are polar (or charged) and regions that are nonpolar are called amphipatic or amphiphilic.

43. Water undergoes ionization • Water is the biological solvent. • Pure water contains not only H2O, but also equal concentrations of hydrated protons, hydronium ions (H3O+), and hydroxide ions.

44. Ionization of water Keq = 1.8 x 10-16 [H2O]=55.5 M because (1000g/L)/(18.015 g/mol) (55.6)Keq = [H+][OH-] (55.6)(1.8 x 10-16) = [H+][OH-] = Kw Kw = 1.0 x 10-14 = [H+][OH-]= [H+]2 [H+] = [OH-] = = 1.0 x 10-7 M [H+] = [OH-] Neutral solution [H+] > [OH-] Acidic solution [H+] < [OH-] Basic (alkaline) solution

45. [H+] pH 10-14 14 10-13 13 10-12 12 10-11 11 10-10 10 10-9 9 10-8 8 10-7 7 10-6 6 10-5 5 10-4 4 10-3 3 10-2 2 10-1 1 100 0 • 1 M NaOH • Ammonia • (household • cleaner) • 7 • Acid • Base • 0 • 14 • Blood • Pure wate • Milk • Acidic Neutral Basic • Vinegar • Lemon juice • Stomach acid • 1 M HCl pH Scale The pH of some aqueous fluids.

46. pH scale • H+ • H+ • H+ • OH • H+ • Lemon juice, gastric juice • H+ • OH • H+ • H+ • H+ • Grapefruit juice, soft drink • Increasingly ACIDIC • (Higher concentration of H+) • Acidic solution • Tomato juice LE 2-15 • Human urine • OH • OH • NEUTRAL • [HOH-] • Pure water • OH • H+ • H+ • Human blood • OH • OH • H+ • H+ • H+ • Seawater • Neutral solution • Increasingly BASIC • (Lower concentration of H+) • Milk of magnesia • Household ammonia • OH • OH • OH • H+ • OH • Household bleach • OH • OH • H+ • Oven cleaner • Basic solution

47. Dissociation of weak acids • An acid is a chemical species that can donate a proton (H+), and a base is a species that can accept (gain) a proton, according to the common Brnstead-Lowry definition.

48. Functions of [H+] • [H+] and therefore pH is important for many biochemical processes: • Transport of oxygen in blood • Enzymatic reactions • Generation of metabolic energy during respiration and photosynthesis • Metabolism and its regulation. • Measurement of pH of blood and urine are commonly used in medical diagnoses.

49. Types of acids

50. Titration curve